How to configure the failsafe dsm2?

If you read the manual for AR6210 -

"The AR6210 features SmartSafe failsafe. SmartSafe is ideal for most types of aircraft. With SmartSafe, when signal is lost the throttle channel only is driven to its preset failsafe position (normally low throttle) while all other channels hold last command."

If you need preset failsafe for all channels, you need other Rx. At least it will be AR7010, AR8000 or higher.

On most AR receivers with preset failsafe this is done by turning on the Rx with the bind plug in place, REMOVING THE BIND PLUG BEFORE TURNING ON THE TX, and then turning on the Tx in bind mode.

or exactly

Preset Failsafe
If the signal is lost, all channels are driven to their failsafe position set during binding. Preset Failsafe is ideal for sailplanes, as spoliers can be deployed during loss of signal, preventing a flyaway.

How To Program
1. Insert the bind plug and power on the receiver.
2. When the receiver LEDs blink, indicating bind mode, remove bind plug before binding the transmitter to the receiver.
3. LED lights will continue to blink.
4. Move transmitter’s control sticks and switches to the desired Preset Failsafe positions, then turn it on in bind mode.
5. The system should connect in less than 15 seconds.

Once again, AR6210 has preset failsafe on throttle channel only.

You can use other channel for the throttle, and set the throttle channels failsafe value to equal to the RTH value...

Yep, that's what I meant to do...
I'm glag it worked.