Migrating unhashed repositories in 16.6

When runnning gitlab-rake gitlab:check, I get the warning that not all repositories are in hashed storage (which is true), and that I should run the migration command (which has been removed since v14). I do not know why these projects weren’t migrated when we upgraded to v14 some time ago, but now I’m not sure if it’s still possible to migrate them to hashed storage. Any ideas would be greatly appreciated. Gitlab is running in the official docker container, if that’s relevant.