GH4 and Rode_How can I record audio as 2 mono channels

I saw this done in an online video a while ago and now, for the life of me, I can't find that video. It showed how to record two separate mono channels from a single stereo input to the GH4. And it showed how to set different levels for the two channels. This allows setting one channel at a "normal" level and a second channel lower. It's a safety measure in the event of unexpected loud sounds that may cause distortion in the primary channel. Does anyone know how to do this?

Thanks