Hi @denis
The custom query should be placed in the template you use to show the map. To learn more about WordPress template, please take a look at this page: https://codex.wordpress.org/Templates.
I’m afraid this kind of customization is a little bit advanced. If you don’t know anything about programming, I suggest you hire a developer to help you out with it. I’d recommend looking for one on https://studio.envato.com/ or https://www.upwork.com/.
Hope this helps!
