Looks like a very generic, cheap budget flashlight.
Seems surprising that you would be able to fit 2x18650 inside the battery tube if the light wasn't designed for it. There's no possible way you could "accidentally" stick 2x18650 into a light designed for one 18650. I assume the problem is either cheap batteries or a short in the light itself. The light can be repaired ... but doing so likely means replacing the batteries, driver and possibly emitter. It may be easier to just buy a new light.
Converting the light to run on AA isn't really a practical option because 18650 are significantly wider and longer. A hobbyist could mod the flightlight to run on 2xAA, but doing so would require a lot of work. You'd need a new driver (the circuit board at the front of the light that the battery sits against). The tube would probably have to be cut down and new threads cut, which would require a lathe. And even if you did do all that, the tube is so much wider than needed for AA, you'd have to add some kind of plastic tubing on the inside of the battery tube to keep the batteries in place. You could skip cutting down the tube by adding a dummy cell in the battery compartment, but that's just extra bulk to carry around.
The conversion could be done... but it wouldn't be easy, might require special equipment and would leave you with a 2xAA light that is much bulkier than it needs to be.