Hi,
I can try to help on this customization.
There are bunch of different templates that coding might go on. I would look in this directory starting with this file:
\wp-content\plugins\the-events-calendar-community-events\views\community\edit-event.php
You can follow the Themer’s Guide it will show you where to move the files to your theme to safely edit them:
https://theeventscalendar.com/support/documentation/events-calendar-themers-guide/
Not sure if that coding will work, it looks correct, but I think it will keep all the other countries there.
You may not need it though as you can set the default country for the dropdown here:
Events > Settings > Default Content > Default country Field
Let me know if you have any follow up questions.
Thanks