Remove all text before a colon in a string

Im trying to replace a block with a falling block while also applying motion to it, and to do that I need the blocks registry name but

when I get the registry name of a block it also has "minecraft:" or "mod_name:" behind it, and to summon a falling block that won't work if it has those behind it.

So I need to remove all of the text before and including the ":"

Im open to code suddgestions, Ive already looked up to see if I could find something but Im not one to know where to look.