In order to add your own map to the server, you must first upload it to some hosting that allows you to get a "direct link", you can tell by the name of your map at the end of the link.
For example, you can use sdílej.cz
Then follow the instructions
- Turn off the server
- Click on Configuration files in the main menu
- For the settings.cfg file, click on "Config Editor"
- Check "Use Custom map"
- Insert your link in the Level URL line
- Click on save
- Start the server
