How to repair shed roof felt

This small roof detail causes big leaks during heavy rain. ☔ This is a very common issue I see in older homes. During installation, the upturn of the valley is sometimes flattened so the tiles sit flush. The problem is that during heavy rainfall, water can surcharge and bypass the valley, allowing it to enter the roof space and cause internal damage. In many cases, this can be rectified by re-forming the valley upturn, which is a relatively cost-effective repair compared to ongoing water ingress