How to change (replace) old 'assigned to' user to new user account after migration? any tool that map this process?

[asafysf]

How to change (replace) old 'assigned to' user to new user account after migration? any tool that map this process?
The team members user in the new server are from another domain.

Thanks

[MrHinsh]

Once the migration is complete there is no way to do this!

There is a outstanding #1776 to add functionality for this