Once you have a way to get your two tone audio into the radio, either via injection to the microphone port, or by transmitting an audio file, you can check your linearity. If you have a good double sinusoidal pattern, then you can expect that your transmitter is running in the linear region. Otherwise you can adjust your transmitter, or amplifier and test again.

https://www.youtube.com/watch?v=NapPt2sxBVE

In some cases, you may want to transmit an audio file from your PC on the IC-7300. In this instance, I need to be able to transmit a two tone wav file, to be able to perform a linearity test. This video details what you need to do to be able to build a file that is compatible with the IC-7300.

https://www.youtube.com/watch?v=QsWXcqnrEgk

In one of my previous videos, I covered installing WSJT-X and reconfiguring the radio to talk to WSJT-X. Bob Stothfang in the Icom IC-7300 group on Facebook mentioned that he handles this by using saved settings files on the SD card. This video deals with executing that method. Many thanks to Bob Stothfang.

https://www.youtube.com/watch?v=jvbwBivmTmI