When you migrate to GitHub.com with GitHub Enterprise Importer, user activity (e.g. issues, pull requests, comments) is linked to placeholder identities called "mannequins".
After you've finished migrating, you can "reclaim" those mannequins, linking the migrated activity to users' GitHub.com accounts. As part of this process, users receive invitations, asking them to accept the mannequin attribution.
Now, organizations using Enterprise Managed Users (EMU) can reclaim mannequins immediately, skipping the invitation process. This can be done one-by-one, or in bulk using a CSV.
To use this new feature, you'll need to update to the new v1.0.0 version of the GitHub Enterprise Importer CLI, released today.
For more details, see "Reclaiming mannequins for GitHub Enterprise Importer" in the GitHub Docs.