Repair Gulikit Kingkong Pro 2

Hello, I just bought a Gulikit Kingong Pro 2 because I think the sensor technology would be useful for a travel controller that could end up messing them up but the controller came with an L button that doesn’t work. I was wondering if anyone knew where I could buy this part and maybe if there was a guide on how to replace the L button in this controller. Thanks in advance.