I don't know why Isaac's post needed to be in white, it's just a fact.
Just make sure, you have a good few apples and at least 3 Oran berries. Your partner is quite annoying in this dungeon, because all the wild pokemon seem to gang up on it
I just went around and around until I found the staircase each time :p Sometimes it only takes half a minute.
Just keep pushing on, even if it looks bleak.