From Advanced Custom Field’s checkbox, I need to add something as checked in the checkbox

this is what my code looks like:
Any help will be very appreciable.

    <?php
        $btn = get_field('line_btn');
        if( $btn && in_array('study', $btn ) ) { 
          echo 'study';
        }
        elseif( $btn && in_array('help', $btn ) ) { 
          echo 'help';
        }
        elseif( $btn && in_array('study', 'help', $btn) ) { 
          echo 'both selected';
        }
      ?>