Lift the edge of the tape up to ensure the resin doesn't get on the rest of the board. Use a tongue depressor to mix and apply to fill the hole completely. When the cabosil starts to set, use a razor blade and sandpaper to trim the excess down to the edge of the hole. A final sanding will smooth the repair edge after the resin has completely cured. After the resin is completely hard, wet sand with fine grit cloth and buff to finish.
Fin repair is nearly as complicated as putting a fin on the board during glassing.
If the old fin is cracked along its base, it must be removed by sanding. Use a 7 inch sanding disk, and sand straight down on the resin area around each fin base until the fin can be remove with a slight tap. There will likely be a hole in the foam under the fin, and this is to be filled the same as any other puncture ding. Also sand the fin sides and bottom to remove excess resin buildup. Position the fin on the board using non-hardening resin to tack the bottom down.