How to add custom search type in Dokan plugin store listing?

At the moment I’m trying to modify the Dokan plugin to work with custom search. As you see from the following figure I added input tag for location:

enter image description here

but, I cannot find which function they use. In store-lists-filter.php file, they have

<form role="store-list-filter" name="dokan_store_lists_filter_form" id="dokan-store-listing-filter-form-wrap" style="display: none">

however, I could not find the responsible function to handle it. To conclude what I’m trying to do:

  1. Make store-listing page custom to work also with the location.