Can I cycle with osteoarthritis in knee or will it damage it more

Low impact exercise such as cycling or swimming are recommended for those with OA in their knees, but it will depend to some extend on how bad the damage is. Basically if it doesn't hurt, or doesn't result in inflammation afterwards, you should be ok to keep doing it at least in moderation. Your knees will tell you when they've had enough and it's time to scale back.