SQLite database issue

[BlueWhaleYT]

package com.company.app;
import android.content.*;
import android.database.*;
import android.database.sqlite.*;
import android.widget.*;

public class DBManager
{
  
  private DatabaseHelper dbHelper;
  private Context context;
  private SQLiteDatabase database;
  
  // Constructor
  
  public DBManager(Context c){
	context = c;
  }
  
  public DBManager open() throws SQLException{
	dbHelper = new DatabaseHelper(context);
	database = dbHelper.getWritableDatabase();
	return this;
  }
  
  public void close(){
	dbHelper.close();
  }
  
  public void insert(String name, String desc){
	ContentValues contentValues = new ContentValues();
	contentValues.put(DatabaseHelper.SUBJECT, name);
	contentValues.put(DatabaseHelper.DESC, desc);
	database.insert(DatabaseHelper.TABLE_NAME, null, contentValues);
  }
  
  public Cursor fetch(){
	String[] columns = new String[] {DatabaseHelper._ID, DatabaseHelper.SUBJECT, DatabaseHelper.DESC};
	
	Cursor cursor = database.query(DatabaseHelper.TABLE_NAME, columns, null, null, null, null, null);
	
	if(cursor != null){
	  cursor.moveToFirst();
	}
	return cursor;
	
  }
  
  public int update(long _id, String name, String desc){
	ContentValues contentValues = new ContentValues();
	contentValues.put(DatabaseHelper.SUBJECT, name);
	contentValues.put(DatabaseHelper.DESC, desc);
	
	int i = database.update(DatabaseHelper.TABLE_NAME, contentValues, DatabaseHelper._ID + "=" + _id, null);
        return i;
	
  }
  
  public void delete(long _id){
	database.delete(DatabaseHelper.TABLE_NAME, DatabaseHelper._ID + "=" + _id, null);
  }
  
}

I have problem when programming the functions of delete() and update(). I found lots of material to see whether will they solve the problem.

@Override
  public boolean onOptionsItemSelected(MenuItem item)
  {
	int id = item.getItemId();
	if(id == R.id.delete_record){

	  dbManager.delete(_id);
	  this.returnHome();

	}
	return super.onOptionsItemSelected(item);
  }
  
  @Override
  public void onBackPressed(){
	  
	  titleText = findViewById(R.id.subject_edittext);
	  descText = findViewById(R.id.description_edittext);
		
	  String title = titleText.getText().toString();
	  String desc = descText.getText().toString();
	  dbManager.update(_id, title, desc);
	  this.returnHome();
		
	}

private void returnHome()
  {
	Intent home_intent = new Intent(getApplicationContext(), CountryListActivity.class).setFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
	startActivity(home_intent);
  }

the this.returnHome() is working, thus I ensure that the problem is came from the DBManager.
Problem: delete() and update() do not work.
thanks.