The mObridge instruction manual that explains operation is a bit convoluted so follows is a step by step walk through.

Insert key into ignition switch.
This will supply power to the radio head unit.
Turn on the radio (if it wasn’t already on).
Wait for the radio to boot and then wait for
an additional 15 seconds as it will throw
the following error:

Press the button to clear the error.

If the radio head unit is not displaying
this screen then press the Audio
button (step 1) to display it.

Press the CD button (step 2).

The CD screen will be presented.

Note that you will want to be on CD 6
as shown above. The CD 12345 are
grayed.

If this is not the case then push the
button (shown below) to select
‘CD List’ … then rotate the button

until you arrive at the Menu/Aux Audio
line choice. Now press the button once
more to select that option.

The following screen will display next.

Press and hold the ‘ >> ‘ keypad button
to ‘ exit lock mode ‘. You will see
CD 12345 go to grayed.

Now you may plug in your iPod to the
iPod cable if desired.

Button 3 on the keypad is used to
select the Audio src (source)

There are three choices for source:
Aux (analog cable headphone jack)
A2DP (bluetooth digital playback)
iPod (digital iPod cable)

Select the source that you want by
pressing and holding the ‘ >> ‘ keypad
for 2 seconds until the source changes.
Then release. If you want a different
source then repeat the procedure.
Hint: If you didn’t hold the button in long enough
the source might not change as desired.
Instead the ‘ >> ‘ keypad button will scroll
out of ‘Audio src’. So, press keypad 3 to try again.