[2020] Stable Update 1.06

You will find the option in the web interface, settings page of your server. The option is called "mission" and allows you to switch between Chernarus and Livonia.

This issue has been fixed, however an additional download is necessary (~3GB). If the download doesn't start on its own, restarting the Steam client or verifying the integrity of the game files (Steam Library >> Manage >> Properties >> Local files tab) may help.