How to Setup Elevons for RC Plane | Flysky FS-i6X Transmitter Setup 

Try reversing channel 1, and if not works then reverse channel 2, or both channels. If still not solves the problem, go to elevon settings and change 1st value to full opposite, i.e., if its 100 then change to -100 and if -100 then change to 100. Also try this to 2nd value. You can experiment with these settings and will find the correct setting. I also do this and finally I find the right setting. Actually these settings are sometimes different because of different servo positions.