Not sure I understood properly what kind of help you need.
I have a running and updated NXT wallet, but what should I do when I'll eventually receive those NXT?
It's not actually a help with no reward but he's trying to sell those 5500 nxt that he have left on Polo. But the problem is that I don't understand either that why is it that it needs to have a message before withdrawing?
I haven't used polo for a long time does this 'message' lies on their exchange or required by nxt wallet?
Also, as someone already suggested, why don't you sell those NXT on polo for another coin and withdraw that last one?
Yes, much better to solve it through this.