Hello there I've got a new device hAP mini and I've tried OpenWRT but I want to return to RouterOS. I've lost my license key because I don't save it before installing OpenWRT, was my fault.
Simply after the successfully restore of the RouterOS,
register here: https://mikrotik.com/client
after that go to https://mikrotik.com/client/keyRequest
and insert your Serial Number and Software ID,
you give back already existant licence to put back on your RouterBOARD