You can buy new felts (they work better when new) in a kit with barge cement for about 25 bucks on line. The barge cement is what you need for repair also. Read the instructions and follow them. I use duct tape wrapped around the repair to apply pressure until it's completely dry.
Shoe Goop is more readily available, but not quite the long term repair barge cement is in my experience. It works, though. Make sure the felt is well attached beyond what's flapping and clean both surfaces well.