gitlab export/import: how to preserve users?

https://gitlab.com/help/user/project/settings/import_export.md:

Group members will get exported as project members, as long as the user has master or admin access to the group where the exported project lives. An admin in the import side is required to map the users, based on email or username. Otherwise, a supplementary comment is left to mention the original author and the MRs, notes or issues will be owned by the importer.

i do not understand from the documentation, what is needed to export project and import so that ticket comments do not get the supplimentary comment. what is "admin" in that context? admin user? user having admin role? sysadmin? where's the "mapping" dialog? can the user be mapped later after import?

i created same login and email to target system but it still created issue note as root user not as the actual user.