I have a Tactic tx660, which im sure is similar to the tx650. I purchased plane that uses 2 elevator servos. 1 for each side. I set wing type to 2 ele. And 2ail. I set the 1st servo on channel 2 and tried to set 2nd elevator servo on channel 5 and also tried on channel 6. Elevators move in opposite directions. I tried to use reverse on the transmitter on channel 2, 5 and 6 separately, and elevators are always opposite. I know i can always change the control rod on the opposite side of the servo. But previous owner of plane had it set without changing servo arm side, and he had a different type radio, but im assuming this should be possible on this radio. Any ideas?

buy one different brand servo that rotates the opposite direction?

I bought these: 5PCS 3.6V-24V Servo Signal Reverse Support High Voltage Compatible for All Servo RC Parts from Toys Hobbies and Robot on banggood.com
https://banggood.app.link/rxYheMkO70

If you can solder, you can electrically reverse a servo. It's just switching two connections, so 4 solder joints total.

Page 16 of the manual covers dual elevator setup on the TX660. Channel 2 & 6 are what Tactic assignes for dual elevators, just reverse the channel that's going the wrong way. Taking a look at the servo monitor screen can be a help for a situation such as this.
Pete