How do I use expansions on my server. I want to run primitive plus but the only way I seems to be able to do it is from the mods. However when I try it that way the server crashes, is there a way to run expansion like you would change a map or something?

Primitive Plus is a total conversion mod. It allows NO other mods due to this. Since it allows no other mods, you may only run P+ with the basic ARK maps.

It is recommended you NOT use Primitive Plus with Extinction Aberration Scorched Earth Ragnarok

As those maps may not include basic requirements to survive with Primitive Plus.