It's in the mixing console located to the left of the screen. Push the button several times to scroll thru the various mixer menus - it waill stay where you leave it, so each time you go back ....you're at the same spot you left. Just remember to "select" the line you need to edit using the a-j keys. Then the keys at the bottom of the screen will change parameters.
Tip o' the day:
Whenever you edit a parameter, the data wheel then becomes the controller for that edit. It makes large changes possible at greater speeps. eg:
Push tempo - the display shows the current tempo .... then the wheel becomes a tempo wheel - until you exit out of the function.
The data wheel wears many hats.