Some of my keyboard keys don't work properly

Hi, I've bought a Razer Cynosa Chroma last year and it worked properly, but recently the C key started to malfunction. When I pressed it, it did not write the C letter. Upon checking on an online keboard tester, I found that when I pressed the C key, it pressed the Alt key at the same time, so the C key was impossible to use. The other keys seem to work fine, though.