You can head to your Space dashboard to add Admins/Owners and Builders to your space.
If you get an error saying their emails are not recognized, that means they have not created an account with Gather yet. Please ask them to head to https://gather.town/app to sign up.
Please note that if you add multiple Admins and/or Builders, you cannot have the Builders working on the same map at the same time. If one person clicks Save in the mapmaker, it will override any map edits being made at the same time by other map Builders (through mapmaker and build tool).