RUM - move migrated computer back to the source domain ?

We successfully migrated  a SQL server into the target domain, but now nobody can connect into the database.  I believe we need to move that server back into the source domain to setup the proper SQL permissions before we migrate that server again into the target domain.  (we didn't check/enable sidhistory during migration).

How do I undo the migration for a computer or revert back the changes?  I see there is an option to revert back processing, but not sure if that's the right course of action.  Seems like we need that server back into the source domain to setup the proper permissions before migration.

Thanks.