Well, here is the walkthrough:
Open Planemaker
Load the B733.acf
Go to the tab "Standard" - pick option "Viewpoint"
Stay in the tab "General", look at the "Cockpit" section (top right)
Locate the fields that say long, lat, vert arm pilots viewpoint.
Change the numbers in those fields to shift the viewpoint long(itudinally), lat(erally) and vert(ically).
Click on the little "x" in the bar above when done.
Choose "File", then "Save" then "Exit".
Now reload the 737 in X-Plane from the developers menu, otherwise you won´t see the change.
Cheers, Jan