The FCC doesn't transfer licenses. If the license was from the prior owner, that prior owner should have canceled the license when the boat was sold.
If you have an RRO, you may already have a Federal Registry Number (FRN). You can get this off you RRO, or you can look it up on the FCC website. You just need to get your password, and everything else is pretty straight forward. Just take your time, and make sure all the information is entered correctly.