VoiceChatMode 

Namespace: SynicSugar.RTC

public VoiceChatMode VoiceChatMode;

public enum VoiceChatMode 
{
    /// <summary>
    /// Automatically transmits voice when detected. Transmission stops when no voice is detected.
    /// </summary>
    VoiceActivated, 
    /// <summary>
    /// Transmits voice only while the specified key is held down. Transmission stops when the key is released.
    /// </summary>
    PushToTalk
}

Description 

Switch OpenVC and PushToTalk.
This is valid only before matching. If we want to switch that after matching, call ToggleLocalUserSending() by ourself.

using SynicSugar.RTC;
using UnityEngine;

public class VCSample : MonoBehaviour {
    void Start(){
        //Push to Talk
        RTCManager.Instance.VoiceChatMode = VoiceChatMode.PushToTalk;
    }
}