Migrating Users From Self-Hosted Gitlab Instance

In the docs for import/export it states:

This approach assumes all users from the self-hosted instance have already been migrated. If the users haven’t been migrated yet, the user conducting the import will take the place of all references to the missing user.

I have looked everywhere but I can’t seem to find any information on HOW to migrate users. Is there a feature in the web interface somewhere? Do I have to create some sort of custom script using the api?