The filter hook is “wp_travel_archive_itineraries_col_per_row” within the folder wp-travel\inc\class-shortcode.php using which you can change the no of column.
If you directly modify your original plugin file then all of your changes will be lost upon update of the plugin to the new version. So we strongly recommend you to go through the child theme for any code customization within the plugin.
The above solution we have mentioned can be executed using the child theme.
For this just create the child theme of your existing theme and paste the above-given code in your child theme functions.php file and it will work.