Realtek Microphone "Set Default Device"

Hello. I've got a basic problem I guess: I messed up with the Realtek microphone settings and selected "Set Default Device". I tried to fix it but I kinda destroyed my mic. - friends tell me they can hear me like I'm closer to them and they hear me worse than before. I just need to unset the Set Default Device thingy but I don't really know how.. any idea?
 
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