Your post was in the Futaba manufacturer's rep forum. I wanted to reply to your question there, but only the Futaba reps can post an answer there. Next time post your question in the general radio forum instead.

Now that your question can be answered by anybody instead of just Futaba reps, here's my answer.

The 9C and 7C referred to flapperons as flapperons, so it was easy to find and setup.

The 12FG uses a combination of WING TYPE and CAMBER menus instead. They do the same thing as flapperons (and more), but with different names.

First, go to the LINKAGE menu.
Select MODEL TYPE.
Under WING, select 2AIL.

Next, go to the MODEL MENU.
Select ELE->CAMBER.
On screen 1/3, adjust the RATE A and RATE B values to get the flapperon deflection you're looking for.
On screen 3/3, set the desired switch to activate the flapperons.