Please add this code int the booking form at the Booking > Settings > Form page, for ability to deselect dates in calendar by clicking on "Deselect" button:
<a href="javascript:void(0)" onclick="javascript:reset_days_selection( this );" class="btn">Unselect Dates</a> <script type="text/javascript"> function reset_days_selection( el ) { var br_id = jQuery( el ).closest( 'form' ).find( 'input[name^="bk_type"]' ).val(); wpbc_unselect_all_days( br_id ); if( typeof( showCostHintInsideBkForm ) == 'function' ) { showCostHintInsideBkForm( br_id ); } } </script>