Make sure the car is stationary and the wheels are pointing straight forward.
Move to gear position D.
Depress the brake pedal fully.
Then fully depress the accelerator pedal.
Release the brake pedal within 2 seconds.
If the Launch function does not work, wait a few minutes and let the drivetrain cool down to working temperature before retrying.
The drivetrain is subject to wear and tear when using Launch and therefore the function is only available a limited number of times.