How do I get a restraining oerder for an abusive adult child living in my home?

Have they been arrested? What type of abuse is occurring?

Call the police to report the abuse then go to court for an RO

Where is this located at, laws differ by location

If there is proof of the abuse, go to the sheriff office or the court house ( where you file differs by location.

What type of abuse, has the police been called. Have you gave them any notice to evict them ?