First, don’t let it scare you. It’s not difficult to do. First, cut away the old fiberglass that encases the wood, then remove the wood. Clean the surface by sanding it smooth to an area about 3 times the width of the wood that you’ll be replacing. the old fiberglass may give you an idea of where you need to prepare to.
You’ll need to replace the wood. If it’s teak it will cost you. I’d be inclined to make a rigid foam laminate as it will be much cheaper. Simply layer some rigid foam and fibreglass into a multi-layer sandwich. Then, cut it to the desired shape.
Once that’s done, it’s time to fibreglass. You have two choices – polyester and epoxy. Polyester is cheap, but epoxy is easier to work with…much easier, and doesn’t smell. YouTube is full of videos explaining how to do this step.
Good luck, and feel free to ask if you need help.