Your code line doesnt work.
I thought you made a mistake, forgetting : #" data-post_id=" in the code line you sent.
Did you mean : <a href="#" data-post_id="<?php echo esc_url( get_permalink( $acc_id ) ); ?>"><?php echo get_the_post_thumbnail( $acc_id, 'biggallery-thumb' ); ?></a>
BUT STILL WITH THIS NEW LINE APPLIED, IT DOESNT WORK.
Please check it out,
Please also send the line of code to do the same modification for TOURS and CARS (click on image leads to item (and not gallery).
Have a good day