You're on the right track...with a pair of channel lock pliers, grab the button and pull straight back. Once the button is removed, there is a hex fastner that is removed. The controller handle will then slide off the splined shaft. If your controller is original equipment, it likely is a Quicksilver Commander 3000 control. If you do a google search for Commander 3000, there is a nice exploded view of the controller on the Crowley Marine link (first link listed after a search) The 3 screws that won't budge possibly hold the shift cassette to the control handle. If you are going to be test shifting the controller, you should disconnect the throttle & shift cables. Makes it easier to shift without the outdrive binding.