If you have previously recommended this thread, you should see a tick / check mark on the recommend button. Click the tick to undo the recommendation (the tick may appear to change to a cross as you do this.) If you added a comment with your recommendation, you will need to delete that from your facebook wall separately.
I see the first one is now full and not accepting any more posts. Are you going to start a second one, which will also be 'stickied'? I'm still waiting (along with others, I suspect) to post my thanks - pending receipt of Secret Santa. I'd hate for my SS to think I'm not polite enough to say 'thank you'.