Dude! Condolences on your loss! I was where you are last September ... 2017 GTR 230. Melted cyl 1 piston. Is the 2019 the 1503 or 1630 engine? Which cylinder has the damage?
1st. I know the owner's manual says you can run 87 octane fuel, but everybody I've talked to in the Sea-Doo community advises against this. Run premium fuel.
2d. My machinist took 1 look at my block/piston, and said "LEAN". Meaning the cylinder fuel/air mixture was lean and it melted the piston.
In my attempt to get to the root cause of the problem, I took two of my fuel injectors to Pensacola fuel injection, one from the damaged cylinder and one from a good cylinder, both flow rates checked the same at 5 different pressure settings. The tech didn't rule out that the fuel injector may have been intermittently clogged/restricted.
Get a Can-Doo Pro or BUDS and check the last few minutes of engine operating parameters. Look and see what your engine coolant temp was; make sure your coolant temp was >190 deg F. According to the BRP service manual, these engines run lean until the engine reaches operating temp (as reported by the coolant temp sensor). Running lean helps the engine warm up faster, but if the coolant temp sensor is lying to the ECU, it could drive an unwanted lean condition (in theory); I've discussed this with other forum members, and that seems improbable if only one piston melted.
In my case, when I rebuilt the engine I changed the #1 cylinder fuel injector and the coolant temp sensor as precautions. Did your burn through the cylinder liner?
Lastly, your cylinder head will have to go to the machine shop so they can clean up the valves and valve seats.
I've got 12 hours on the new engine, and it's running like a stabbed rat! Cost me about $4300.00 to rebuild it myself.