I’m not really all that familiar with that plane, but there should be an audio panel somewhere that lets you select COM1 / COM2 for transmit & recieve. You can only transmit on 1 channel at a time, but can receive from both. You need to find the button to shut up the second radio when this happens.
And again, depending on your plane, that will be different. The G1000 planes are on the strip between the PFD and MFD (top 4 buttons). On the steam guage C172, it’s the unit at the very top of the radio stack. On the G3000, it’s in the comms menu from the touch screen. On airliners, I don’t know. I don’t fly those.