What do you want to achieve ? Do you want to run the two motors from one stick ?

My understanding of V-Tail mixing is this:

On a standard plane, there are two perpendicular control surfaces for the tail, a vertical rudder and a horizontal elevator.
These are controlled by a servo each, say from one stick.
When the stick goes forwards and backwards, the elevator goes up and down. The rudder doesn't move.
When the stick goes side to side, the rudder goes left and right. The elevator doesn't move.

On a V-Tail plane, there are two inclined control surfaces for the tail which both act as both rudder and elevator.
Now when the stick goes forwards and backwards, both surfaces go up and down.
When the stick goes side to side, both surfaces go left and right.

This means each servo must be controlled from both channels, hence the need for a mixer.

The default channels for elevator and rudder on your transmitter are 2 and 4, so you'll need to move to these channels. You should then find that the right stick controls both motors. I would guess that stick forwards is both motors forwards, stick backwards is both motors backwards, stick left is one forwards and one backwards and stick right is the opposite. Not sure what your hover will do when you do that though !!

Disclaimer: This is all theoretical as I've never actually used this function ;-)