How do I reverse the elevator & aileron controls in the elevons on a mode 2 TX

What mode 2 transmitter? Be specific.

Its not very clear what you're asking. Are you saying that currently your transmitter elevator command results in a roll and an aileron command results in a pitch change? With elevons, your aileron and elevator controls get mixed in the transmitter. Most transmitters have a unique, pre-defined function for elevons. We would need to know exactly what your issue is and specifically what transmitter make and model you're working with to provide any help.

Some transmitters have dip switches. Others you program the servo reverse. It depends on the transmitter