How to add custom code for plugin to the Enfold child theme

A while ago a webdeveloper added some custom code to the files of the WP Store Locator plugin to display a phone number in the list view.

I would like to move these edits to the Enfold Child Theme to make sure the edits won’t get lost after updating the plugin. But I am not sure how to do this. After trying some different ways to make this work I hope you can help.

The files from the WP Store Locator plugin which has been edited I have duplicated to my own computer. The edited files (normally these are in the wp-store-locator folder) are:

frontend (folder)
– underscore-functions.php (file)
— templates (folder)
— store-listings-below.php (file)
— default.php (file)