Cut a square with clean lines, what you want to do is to remove all the torned and split wood away, first draw a square shape with a pencil, then using a new (as in very sharp) Xacto knife with a # 11 blade cut the wood where the pencil lines are, start prying of the damaged wood little by little, try to remove as little foam as possible, cut a piece to fit the area of the leading edge first by using the same size material if possible, this will avoid having to sand to shape later and glue in place using any of the sandable carpenter's wood glues, after it dries, cut a piece of sheeting to fill the rest of the cut out, also use aliphatic glue, if there is too much foam missing, and the sheeting is say 1/16 thick balsa, use a little thicker, maybe 5/32 to add some more rigidity to that area, sand even, and then recover, don't worry about replacing the lost foam, if it were a very big void, I would then cut a piece of foam and glue in place and proceed with the leading edge and then with the sheeting but in this case it is not necessary, good luck!