Two bits of advice and a question first. What did you add to the tank water just before this happened?
I can't help you obviously if the skimmer has already flooded, but have my sump sitting in a larger plastic tub
to trap uh-oh water. It is a pain but I guess it serves a purpose. If your skimmer just won't stop flowing you need
to stop the air flow to it temporarily. I know zip about RO skimmers, but I am just trying to help in a general way.
What happened? Did the skimmer cup overflow (that would mean it is adjusted incorrectly and pulling too much water into it) or did it leak from the connections?