I used to have massive IT band issues… buy a foam roll, and follow these instructions.
This will alleviate the symptoms, and loosen the tendon over time so the symptoms become less and less. They key to the foam roller working is time + consistency.
But you will definitely want to find the underlying cause - for me, it was bad running shoes exacerbated by a outside (supination) foot-fall. If you are having IT band issues on the bike, I’d start with cleat placement and/or arch support, and work up the leg from there in terms of diagnosing.
Good luck