I have a small red dot in the footage after I capture it. It shows up more when its dark.

What can I do?

Sounds like a bad pixel. If the dot shows up even worse at high gain then you most definitely have a pixel going bad or already gone. Try a couple of black balances if your camera will do that and see if that clears up the problem. If not your probably just out of luck. Broadcast cameras will often allow you to remap bad pixels but I don't think the XL1 does.

High gain, slow shutter speed, and low light or dark situations with simple/flat image backgrounds can cause bad pixels to show up or become more apparent in an image. One way to address this in post is to make a pixel mask to hide the red pixel when you edit.