Cant figure out the deathly hollows sword and locket part – LEGO Harry Potter: Years 5-7 Review

I'm really frustrated because I'm not sure how to get past the part where Ron and Harry are on land destroying the locket! All I get is Ron and Harry then moving the rock to get half of the block up so Harry can open what ever is there
Review by Bdesersa on LEGO Harry Potter: Years 5-7.