You can position your forearms under the spoiler to lift upwards and at the same time your hands to grab the leading edge of the spoiler backwards, and tilt up the spoiler to its full 90 degrees as if the air brakes are fully engaged.

The spoiler will settle down after you start the car and drive off.
If you are planning to unscrew and remove the spoiler from the hinges, disconnecting and reconnecting the cables, do ensure the car is completely 'shutdown' otherwise it will throw up several fault codes.

The spoiler will return to its lowest point after you start the car and drive off but it may constantly tilt ever so slightly up and down because the tilt hydraulic sensor has not been properly reset. It will indicate "Air Brakes Failure - Return to McLaren Dealer'.
