First you need to locate your Cruise Meet thread.
1) Look for the thread that's titled "Find your (year) (ship name) Cruise Meet LINK here". Click on that.
2) The first post on that thread will have a list of the various cruises that ship is taking that year. Scroll down to your cruise date. If there's a Cruise Meet thread started, there will be a link posted underneath the date.
3) Click on the link (if there is one). Fish Extender groups are handled on Cruise Meet threads.
And when I have found it, what do I do ?