Beach shores + ocean problem

hello

i have an island that holds the main map in my game, but i have a problem with it
the heightmap i imported did not take in the beaches and decent of the island into the ocean. is there any tactic or trick i can use to fix this up??



i already have an ocean floor part that procedurally generates a few hundred studs below, but i don’t know how i could get the terrain to go down that far