You can upload and use any icon you wish. The icons are URL based and can point to a media file on your WP site.
I do not read the support forum here very often.
If you want a quick response please post in the Store Locator Plus forum at
https://www.storelocatorplus.com/forums/
You will need to be a registered user. Register by “purchasing” the FREE Forum Registration on the site.
https://www.storelocatorplus.com/product/forum-registration/
You can also submit questions via email using the contact form at StoreLocatorPlus.com, but I prefer you use the forums. It helps others find answers to similar questions and keeps my inbox from overflowing. The forums are also answered by several people which means you are not waiting days for a personal response from one of the core Store Locator Plus customer service people.
https://www.ads-software.com/plugins/store-locator-le/
