Are you talking about the insert for the drive shaft seals? (where you clamp the boot)
OR....
are these new threaded inserts for the pump studs?
If it's the pump studs, remove/drill the old ones out, and epoxy in the new ones.
If it's the driveshaft boot instert... then just cut the old one flush with the inside of the hull, and epoxy in the new insert.
Use a slow curing epoxy. First... it will give you the most working time, and second... some of the fast drying epoxies aren't 100% waterproof. (1 hour cure or slower)