There are two ways to import Slack's backup file.
Import dialog will appear when you click team name in viewer.
Import Slack backup file with GUI might be difficult because of its file size.
You can also import the file with ./bin/import.rb
.
$ docker compose cp PATH_TO_BACKUP_FILE logger:/tmp/slack_backup.zip
$ docker compose exec logger bash -c "bundle exec ruby ./bin/import.rb /tmp/slack_backup.zip"