How can I select audio input channels?

Hello,

I am new to Manycam and figuring out how to use audio.
For audio input, I am using an audio interface. My interface has a loopback feature, but the loopback audio always comes in channel 5-6. Is there a way to select channel 5-6 as input in Manycam? I guess Manycam picks up channel 1 by default.

Thanks!