After investigating this a bit more, the reset-admin command is a bit special and bit buggy. It works by starting a Grafana instance and because of that it needs to know where the config file is:
But there is a bug here so the homepath argument does not work.
This command is only supposed to be used when you have lost your admin password. I would recommend using the API instead → User HTTP API | Grafana documentation. Login with basic auth using the admin account and the default password.
Here is how to do it with curl:
curl -X PUT -H "Content-Type: application/json" -d '{
"oldPassword": "admin",
"newPassword": "newpass",
"confirmNew": "newpass"
}' http://admin:admin@community.grafana.com/api/user/password