DIAGNOSIS: This is a physical stress failure. The plastic housing where the barrel connects to the handle has likely cracked or the internal screws have loosened from regular twisting force during use.
FIX: Unplug it and inspect the black plastic neck closely for any visible cracks. If you see a crack, it's only going to get worse. The unit is not safely repairable at home. You should stop using it and contact Revlon.
IF THAT DIDN'T WORK: If there's no visible crack, the wobble might be from loose internal assembly screws. However, accessing them requires disassembling the handle, which is complex and voids any warranty. It's not recommended.
HEADS UP: This often happens from using a forceful, twisting motion while styling. Always guide the dryer with a smooth, pulling motion rather than twisting it like a traditional round brush. A wobbly connection is a safety risk and can lead to an electrical short.