[JKT]

Remove OmniFocus from the phone by unchecking it in the Applications section of your iPhone pane in iTunes when you have the phone connected (then synch it to remove OmniFocus). Then re-install it again by re-checking OmniFocus and synching again. This will be the equivalent of re-installing OmniFocus anew (so you will be able to set it up as if it had never been installed previously).