You'll need to set the "Search Region Bias" in your map settings. You can do so in the MapifyPro > Maps > [specific map] section of your admin.
Note: Per Google standards, you'll want to use the COUNTRY CODE rather than the full country name. So, UK instead of United Kingdom. You can find the full list of country codes here.
This is incredibly useful to make sure MapifyPro searches look at a specific country FIRST before searching others. So if most of your locations are in the United Kingdom, you'll want to enter "UK" in this field on that specific map. Otherwise it will first search the United States, and may display "No results found" when visitors search on your map.
To adjust this settings, scroll near the bottom of your map settings, and you'll see the following field where you can set the country: