Put this into the console:

If that doesn't work:

To spawn the bots:

If you're having some bugs or issues, like being auto balanced or bots not damaging eachother, do this in the console:

Note that this is a LAN server (local area network) and people won't be able to join you unless they're on the same network, you'll have to port forward and that's a whole other thing
If you don't know how to use or enable the console, you can find it under Options > Advanced

Award this so people can actually see it and figure this out