Rub fabric paint (select one of the more viscose types for silk screen Tshirt printing) with your finger. Take lens out and put finger from one hand under the damaged part of the curtain. Pick a bit of paint with another finger from the other hand. Dab paint on spot and rub it in with your finger until it thins out. Be light fingered at all tlimes!
If the holes are many and the shutter appears to be dry and flaking, patching the hole(s) is just a short-term stop-gap. A shutter in this state will soon be cracking and flaking in many parts. And it happens when you least want it, without even knowing it until you see the developed negatives of your once-in-a-lifetime shots spotted all over with pinhole fog marks.
Shutter replacement is the only reliable measure for cracking dried shutters.
Jay