Not sure you'll be able to do this in V3 so enjoy while you can. Roll your cursor up to HOME, click on live chess, now select Play Now from the list to the right (not the big orange button). OK, now you select time control from a drop down menu that appears under that upside down black triangle. Choose Custom. A Rating Options button pops up. Click that , choose some parameters and you're ready to go. Might take you awhile to get a game. This link has some details.
https://support.chess.com/customer/en/portal/articles/1622811-how-are-seeks-matched-in-live-chess-
I want to play people between 800 and 1000, but don't know where to set it.