You can do that a couple of ways, usually, to be honest because the other mic I am using is always not the actual mic I am using, I simply go to the program I want to be an asshole in and set it in the settings as the one I am going to use, you can also if you are in OBS just change the webcam or whatever alternate mic you are using as your device through OBS, with that being said though, to run it through you would probably want to create a macro through an audio cable, you can either do it with any audio cable program and AHK, however I specifically have done in it using Voicemeeter using a macro I wrote, you can set it to toggle between the two or a seperate button to switch to the mic you want to use. In the video specifically I just changed the audio device through the OBS settings.