Just swap the two cables from Port to starboard and Visa versa. LoL. Simple

The cables get disconnected at the small red circle.
It also looks like you are missing parts that should lock the cables into the notches. Notice the threaded holes.

Its been a while since I've had a set of these in front of me. They really are pretty straight forward though. I think there is just one long threaded rod that goes through all the cable ends(where I had the small circle)that you need to remove. If I remember correctly, there are just some nyloc nuts on each end of the rod.
Before you undo the cables though--label them with a sharpie. Like PS for port shifter and ST for starboard throttle, because they will get all mixed up when they are all disconnected.

Is there a way to tighten the throttle levers on this unit? My starboard throttle slowly falls as I drive around and it is annoying to say the least. Thanks in advance.

the merc controls dont have an arm tension adjustment screw like most other brands have
the throttles have a ball and spring that u should hear clicking as u move the levers
if throttle levers are smooth moving and no clicking then the ball and spring may have been taken out
then would have to dissasemble to put back in and find used merc controls to rob the missing parts to fix yours
as stated on cable swapping after u pull the lower pin holding lower cables in slots
pull cable out of slot and forward till upper cable comes off the lever it has a hook style holder at lever
of coures going back together do in reverse ,,,hook the upper and push lower into slot

Switch them back by motors