SetAudioInputDevice 

Namespace: SynicSugar.RTC

public static void SetAudioInputDevice(AudioInputDeviceInfo deviceInfo, bool isMute = false)

Description 

Change InputDevice. We can also set whether to mute the input device at the same time.
AudioInputDeviceInfo

using System.Collections.Generic;
using SynicSugar.RTC;
using UnityEngine;
public class MicSetting : MonoBehaviour {

    public void Start(){
        List<AudioInputDeviceInfo> inputs = RTCConfig.GetInputDeviceInformation();
        //Mute the device in whole game instead of one session.
        RTCConfig.SetAudioInputDevice(inputs[0], true);
        Debug.Log(inputs[0].DeviceName);
    }
}