Determine your type of knee problem and correct your riding, or do exercises to fix the problem.

A couple of physiotherapist sessions can help find the problem and give you a plan to solve it.

For me cycling, my cleat position was bad on my shoe and my pedals had bad float. The pain went away instantly.

For running, pain felt at the knee was actually from my iliotibial (IT) band and some excercises/stretches the physiotherapist gave me helped that. That took a bit of time.

Most health plans should cover this at least in some part.