unmigrate

verb2

1. •
   (rare) To reverse the process of migration; to switch back to an older system.

   • I could “unmigrate” the tapes, and that would take a while, but it wasn't that much of a nuisance and it helped keep the mainframe's disks free. — 2011
2. •
   To work backwards from the point where an observation was made to deduce the location from which it migrated.