Can I fix a slow spot on my mouse pad?

Probably not. The slow spot is caused by wrist oils, dead skin, and friction that compress the fabric fibers. Washing with warm water and mild soap might help a little, but if the fabric is physically matted down, it won’t recover. Hard pads don’t have this problem as much. In my experience, once a cloth pad has a distinct slow spot, it’s already dying—buy a new one.