it's pretty simple: use F3 to load a map, WASD RF and mouse to navigate around and use the console command PLAY to test it out ingame (also there should be a readme with more keys)
ingame it's the same console command as Lab (MAP mapname) but I just noticed it's seems to be broken using this way.. I'll get back to you on that 🤔
Edit: works fine, I forgot that you need to start a new game for it to work