To achieve what you're wanting, there are just a few steps:

First, put the flaps to VR-D by using the Aux-Ch function on the transmitter.

Now go to the advanced menu and activate the flaperon function. Set the amount of aileron travel you wish. Leave the flaps at 100%.

Activate the Flap Trim function and set how much you want the flaps to be deflected.

Go into the PMix #6 or #7. Go to the second page of the mix and set flaps as master and flaps as slave. Link is ON, and the switch position is Null.

Go to the first page of the mix menu and set the curve. You want one end of the curve to be at -100% and the other end at 0%. Which numbers go where depend upon the exact amount and direction you need to set them up. The easiest way to do that is to move the slider the the flaps up position, see where the index line on the curve graph moves, and then set that number so that the flaperons on your model are at the retracted position. That will be point #1 or #5. Now move the slider all the way down. The opposite point will be highlighted. Set that one to your flaps down position. Now just set the intermediate points so that you have a straight line from point #1 to point #5.

In my transmitter, I wound up setting them like this: #1 at -100, #2 at -75, #3 at -50, #4 at -25, and #5 at 0. Your numbers will be different, depending upon your exact setup.

Remember, get the flaperons working properly first. Then set the mixer curve to suit your model. It helps when you have the model turned on so that you can see what's happening.