Here is the one of the Webniar link (Recorded), it was helped me a lot to understand the Adobe analytics user migration process
Also, here is the community thread landing page URLfor other recorded videos as well.
Hope fully you might understand the each and every process during the migration activity while see those recorded videos. Make sure be active on what needs to be done before the migration, migration in progress and after the migration.
Hope this helps for you and let us know if you need anything else required.