Can you add image to pop up when hover over marker?

Yes, it requires this filter.

If you copy the code in the usage section, replace ‘my_textinput’ with ‘thumb’, then a thumbnail will show up if it exists.

You need to add the code the functions.php in your active theme folder.

Where is the usage section??

https://wpstorelocator.co/document/wpsl_info_window_template/#usage

Where does the code go in the functions.php??