Call a contractor. The only real way to fix it is by removing the siding from above the window and re-flashing it. Removing siding is a pain and once it’s been on a house in the sun and weathered it becomes brittle. I moonlighted for a buddy that ran a siding company for a couple of years and wouldn’t attempt to do it myself. Actually we both know I would because I’m too cheap to pay someone else but that’s just me. LOL