The title is pretty self explanatory. All you have to do is push the Jet Ski off the trailer. But don't just push it off and turn around, or the water will reclaim it. Hold on to it. You don't have to move the trailer out of the water just yet, but if you still have that buddy around it would hurt to move it. Just watch your toes.
If you have a Jet Ski that can reverse, skip this and the next step.