Where wind driven rain is working under the roof and causing leaks then the felt will need to be replaced.
Replacing roofing felt from inside loft.
The rips are small enough that this should be sufficient if you run into a larger rip you may need to choose a different method or support the flashing as it may fall off due to its weight if it s larger than a few square inches.
Is it feasable to restore the missing felt from the inside without removing roof tiles.
To replace a small section of roofing felt involves stripping the tiles from the roof and replacing felt between two joists.
The tiles are the fairly common large concrete type and the roof has 4 x2 rafters and standard 1 battens.
You can purchase self adhesive flashing which in small pieces should adhere well to the felt and should be suitable for the heat and cold experienced as roofing underlayment.
However it can be difficult and unsafe to do it on a ladder but you might find someone who can do it.
The felt near the eaves near the guttering can age faster than felt further up the roof.
A section of the felt is missing from the inside of my pitched tiled roof.