SQLite statement for the update of a database in Android not working

I am new to Android and working on a simple To do list app in Android. Currently, I am running into a problem when trying to update the database with the value of a text field. The function is executed when the user clicks on a button. The value from the text field is fetched, that works fine. The problem is in the SQlite statement, but I couldn´t figure it out until now:

public void saveEntryClickFunction(View view) {

    final TextView textViewToChange = (TextView)   findViewById(R.id.task_description);
    String task = textViewToChange.getText().toString();
    helper = new TaskDBHelper(TaskActivity.this);
    SQLiteDatabase sqlDB = helper.getWritableDatabase();
    String sql = String.format("UPDATE %s SET '%s'",
            TaskContract.TABLE,
            TaskContract.Columns.TASK_DESCRIPTION,
           task_description);
    sqlDB.execSQL(sql);
    updateUI();
}

Any help on this issue would be very much appreciated, thanks!