Domain Controller Policy setting "Allow log on through Terminal Services"

Hi,

I'm just working for three weeks at my new job. I made the switch between
the Domain Controller and the Terminal Server.
I thought a new created user I made was not able to log on to the Terminal
Server.
At first I didn't understand, because the other user were able to log on.
After looking for some solutions I came to a site which adviced me to change
the "Allow log on through Terminal Services" setting with the group "Remote
Desktop Users".
So I added this group as being the only group and activated this setting.
Now I was not able anymore to logon as an Administrator to this server.

How can I undo this setting, is this only possible with a "counter" policy,
or is just deleting the group and uncheck the "activate setting"?

Thank you.

Bram Warrens