The red area with the bird things? If so, then use the ice beam, which you need the speed boost and Varia Suit for, to freeze the bird things, then jump on them. You can’t get back into the green area without the Wave Beam though.

Actually, I got past that part, however I’m completely lost on finding the grapple beam. I beat Crocomire, but still can’t find it.

It should be directly after Crocomire. Explore that area after its room as if you didn't know wall jumping exists.

Well, I've gotten farther, my latest dead end is in lower Maridia, the area with quicksand pits in almost every room, I've been scanning everything and I still have no idea where to go.