From page 30 of the manual:
Setting up the Flaperon function
1. Use the up or down arrow keys to select the FLPR window.
2. When first accessed, the flaperon function is inhibited (INH). Press the CURSOR key to get to the activation menu. The INH indicator will flash on and off.
3. Now press the (+) key to activate the flaperon function. At this time, the ON indicator will blink on and off.

Then from page 31:
FLTR — Flap Trim Function
The Flap Trim function is used to specify the amount of flap travel produced by moving the flap control (the CH6 knob). If flaperon (FLPR) function has been activated, FLTR is automatically turned on. Sailplane folks call this effect “camber,” because the model’s airfoil is changed across the span.
Setting Flap Trim function
1. Use the up or down arrow keys to select the FLTR window.
2. Press the CURSOR key to get to the activation setting. The INH indicator will flash on and off.
3. Now press the (+) key to activate the flap trim function. At this time, the ON indicator will blink on and off.
4. Now you’ll set the flap knob’s travel direction. This is similar to the reversing menu, but it reverses the response of both flaperons if flaperon mode is active.
Pressing the CURSOR key one time causes the large sign in front of the number to blink. You may reverse the travel direction by selecting the minus (–) sign.
5. Pressing the CURSOR key again moves to the flap travel setting number (the percent sign should now be flashing). The 30% default value produces “reasonable” travel for many models, but you must try it out on your own model to be sure. A 100% setting causes extreme travel and is not recommended. You may want to set it to a smaller number, say 10% for starters. If you wish to return to the default 50% setting, press both the (+) and (–) keys simultaneously.

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The copy/paste from the manual is for the transmitter in the picture below.