Stick this felt over your split using bitumen adhesive ensuring there if a 50mm overlap beyond the split.
How to repair split roof felt.
Take the flashing strip off by prising it away from the wall.
If the split or tear can be lifted without causing further damage to the felt carefully lift it and.
Many roofs function quite well without any roofing felt so small tears and damage to roofing felt are not in themselves reasons to spend money on repairing it.
Clean the area by raking out old debris and mortar.
If you have a split in your felt carefully remove the gravel around it.
This area can sometimes come away from the wall allowing water to trickle below the surface of felt.
Holes in roofing felt are quite common here we repair a hole in some roofing felt that is underneath the tiled roof.
Choose a dry warm day to repair the roof.
If an overlap is.
Repairs blisters in the felt.
Acrylic sealant will scrape off and clean with acetone for a permanent repair later on.
Where wind driven rain is working under the roof and causing leaks then the felt will need to be replaced.
Use a ready mixed mortar if only a small amount is required.
Cut a piece of new felt to use as a patch to cover the split.
Then you will need to apply some bitumen adhesive over the split repair.