How do etalus players instantly place ice with up b?

I keep seeing etalus players do up b into a wavedash, and it places ice. But when I try it it only works if I do an up b then wave dash down and diagonal after, and its way slower. If I try to do it instantly it just cancels the up b. If anyone can explain how lmk, or if there’s a tutorial somewhere lmk lol I couldnt find any