It's really hard to say what happened. If the engine was running rich of peak RPM all the time, it should not have overheated, which is what usually causes loss of compression in a ringed engine.

It's possible the engine went overlean from some other factor, and that would cause the overheat. It's also possible that something caused the ring to no longer seal. The engine could have ingested something that scored the piston/ring/liner assembly to the point it won't hold compression, or the ring has broken for some reason. Only a teardown will tell.

No special tools are needed to disassemble and reassemble the engine, but you do have to make sure the ring gap is over the pin in the ring groove of the piston, and that the piston is aligned when you install the liner.

If it's a possible warranty concern, then the engine should come into the service center.