Suspected scammer.
You can't delete an Original Post - However you can Block the member - which will delete the post for all the other members of the group.
That's what we've taken to doing with the scammers who are posting links. Because some of those appear to be malware.
The "Merry Christmas" greetings - are anything but that.
If the comment is in a thread - you can remove it as a Group owner or moderator. And if you suspect a scammer - be sure to report them too.
I guess it was taken care of. The post has disappeared and the member account appears to have been deleted.
@MissKathleen
The trolls/scammers report group?