In MyAdapter, add a field for selected items, since adkr is an array of strings:

Set<String> selectedItems = new HashSet();

Then as @REX says, add an onClick listener to the MyViewHolder but I would alter the approach. I would add a bind method, so it looks like this.

public class MyViewHolder extends RecyclerView.ViewHolder implements View.OnClickListener {

        TextView textView, repeat_Tv;
        LinearLayout layout;
        int position;
        String value;


        public MyViewHolder(@NonNull View itemView) {
            super(itemView);

            textView = itemView.findViewById(R.id.textView);
            repeat_Tv = itemView.findViewById(R.id.repeat);
            layout = itemView.findViewById(R.id.ll_bg);
        }

        public void bind(String value, int position){
            textView.setText(value);
            repeat_Tv.setText(value);
            if(selected.contains(value)){
                // background for selected
            } else {
                // background for unselected
            }
            this.value = value;
            this.position = position;
        }

        @Override
        public void onClick(View v) {
            if(selected.contains(value)){
                selected.remove(value);
            } else {
                selected.add(value);
            }
            notifyItemChanged(position);
        }
    }

Bind it like this:

@Override
public void onBindViewHolder(@NonNull MyViewHolder holder, int position) {
    holder.bind(adkr[position], position);
}

This will allow you to track what is selected and show it appropriately.

You can add clicklistener in your viewholder which will detect the on click events.
code changes will be something like this:

public class MyViewHolder extends RecyclerView.ViewHolder implements View.OnClickListener {

    TextView textView, repeat_Tv;
    LinearLayout layout;


    public MyViewHolder(@NonNull View itemView) {
        super(itemView);

        textView = itemView.findViewById(R.id.textView);
        repeat_Tv = itemView.findViewById(R.id.repeat);
        layout = itemView.findViewById(R.id.ll_bg);
        layout.setOnClickListener(this);

    }

    @Override
    public void onClick(View view) {
        // change background of layout here
    }

}

I have a linearlayout in my recyclerView and i waant to implement on click event on every item, when i select the first item should change the background of the linearlayout of the first item and when i pressed it again returns the first background , i just want to select multiple items not only one can anyone help me with this!!!!

here is my adapter code

public class MyAdapter extends 
RecyclerView.Adapter<MyAdapter.MyViewHolder> {


String[] adkr;
    String[] repeat;
        Animation anim;
            Context co;

public MyAdapter(Context context, String[] all_adkars, String[] all_repeat) {

    co = context;
        adkr = all_adkars;
            repeat = all_repeat;

}


@NonNull
@Override
public MyViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {

    LayoutInflater layoutInflater = LayoutInflater.from(co);
        View view = layoutInflater.inflate(R.layout.custom_list, parent, false);

    return new MyViewHolder(view);
}


@Override
public void onBindViewHolder(@NonNull MyViewHolder holder, int position) {

    holder.textView.setText(adkr[position]);
        holder.repeat_Tv.setText(repeat[position]);
            setAnimation(holder.itemView,position);

}

@Override
public int getItemCount() {
    return adkr.length;
}


public class MyViewHolder extends RecyclerView.ViewHolder {

    TextView textView, repeat_Tv;
        LinearLayout layout;


    public MyViewHolder(@NonNull View itemView) {
        super(itemView);

        textView = itemView.findViewById(R.id.textView);
            repeat_Tv = itemView.findViewById(R.id.repeat);
                layout = itemView.findViewById(R.id.ll_bg);

    }


}

private void setAnimation(View viewToAnimate, int position) {


    anim = AnimationUtils.loadAnimation(co, R.anim.list_anim);
    viewToAnimate.startAnimation(anim);


}

}

Here is my custom list xml code

 <?xml version="1.0" encoding="utf-8"?> 
 <androidx.constraintlayout.widget.ConstraintLayout 
 xmlns_android="http://schemas.android.com/apk/res/android"
 xmlns_app="http://schemas.android.com/apk/res-auto"
 xmlns_tools="http://schemas.android.com/tools"
 android_layout_width="match_parent"
 android_layout_height="wrap_content"
 android_paddingBottom="20dp"
 android_id="@+id/rl_item"
>



<androidx.cardview.widget.CardView
    android_id="@+id/card_view"
    android_layout_width="match_parent"
    android_layout_height="wrap_content"
    app_cardCornerRadius="20dp"
    android_layout_marginTop="20dp"
    android_layout_marginBottom="20dp"
    app_layout_constraintBottom_toBottomOf="parent"
    app_layout_constraintEnd_toEndOf="parent"
    app_layout_constraintStart_toStartOf="parent"
    app_layout_constraintTop_toTopOf="parent">

    <LinearLayout
        android_id="@+id/ll_bg"
        android_layout_width="match_parent"
        android_layout_height="wrap_content"
        android_background="@drawable/gradient"
        android_orientation="vertical"
        android_padding="10dp">


        <TextView
            android_id="@+id/textView"
            android_layout_width="match_parent"
            android_layout_height="wrap_content"
            android_fontFamily="@font/shorooq"
            android_textAlignment="center"
            android_layout_margin="5dp"
            android_textColor="#CCFFFFFF"
            android_textSize="20sp"
     />

 <Button
 android_layout_width="match_parent"
 android_layout_height="2dp"
 android_background="@drawable/repeat"
 android_layout_marginTop="15dp"
 />

        <TextView
            android_id="@+id/repeat"
            android_layout_width="wrap_content"
            android_layout_height="wrap_content"
            android_fontFamily="@font/shorooq"
            android_textAlignment="center"
            android_layout_gravity="center"
            android_layout_margin="5dp"
            android_textColor="#BFBB8763"
            android_textSize="25sp"
       />



    </LinearLayout>
  </androidx.cardview.widget.CardView>
  </androidx.constraintlayout.widget.ConstraintLayout>