If a bulkhead has moved from where it used to be, hire a professional to fix it. If it is remaining in its original position and only its tab is damaged, conduct the repair yourself. To repair a loose bulkhead on a boat, try to open and clean out the gap between fiberglass tabbing and the bulkhead. Use a vacuum cleaner to do this, and make sure that there is no dust, dirt, fiberglass pieces or broken wood splinters left.
Drill holes around the tabbing, placing them 4 to 6 inches apart. Place screws into the holes, and make sure that their tips aren't showing on the other side of the surface. Place some epoxy, hardener and high-density filler in a bowl, and mix these materials well to create resin. Stuff the mixture between the bulkhead and fiberglass tabbing. Use a putty knife for this, and make sure to put on gloves and a chemical respirator. The mixture hardens very quickly, so mix a small amount of it at a time, and work quickly. Don't use the resin once it gains a rubbery consistency.
Tighten the screws you have installed, and clean out any excess resin using a putty knife. Wipe the area with an acetone-soaked rag. Make sure to use a respirator and gloves.