Go to the All Apps section  and open Settings then  Q key.

To pair a functionality or app to a type of push (quick, double or long) using the quick access button:

1. Turn on the Q key feature.
2. Press the left part of the screen.
3. Select the functionality or app to be paired with the push.

You have also access to other settings for the Q key through the setting icon located in the upper part of the screen.