Step 1: Navigate to the Game Panel and Login
Step 2: Navigate to the File Manager
Step 3: Navigate to this File Pathway: (/home/container/garrysmod/cfg/server.cfg)
Step 4: Configure Your Server Location
Change the "sv_location" variable to include the ISO code of the country you would like the flag to display on the server browser. You can find a list of ISO country codes here, just "Ctrl+F" and search for the name of the country flag you want to use. Common ones include...
United States: US
Great Britain: GB
Australia: AU
France: FR
European Union: EU
Step 5: Save Your server.cfg File/Restart Your Server
Save your server.cfg file and restart your server.