ChangeOutputVolume 

Namespace: SynicSugar.RTC

public static void ChangeOutputVolume(float changeRate)

Description 

Change output volume.
0 is mute, 50 is not changed from source value, 100 make volume double.

using SynicSugar.RTC;
using UnityEngine;
public class MicSetting : MonoBehaviour {
    public void Start(){
        //Make output value double.
        RTCConfig.ChangeOutputVolume(100);
    }
}