With "on the top left of the status, channel option thing", you mean it is in the channel window system menu.

Each window has a system menu. The system menu button is the little thingy in the top left hand corner of a window ie. the button you usually double-click to close a window. Click it once with your left mouse button.Alternatively type Alt - (alt + minus). It will popup the usual system menu (with options to move, minimize, maximize and close) but with a few added functions (these vary depending on the type of window).
Each channel window system menu has a 'Nick list..." item leading to a dialog with the 'Auto-hide nick list' option.