Create a new allocation
This will provide your server with another accessible port, which VoiceChat can use.
Go to your voice chat configuration
Now that you have a new port that is ready to be used, navigate back to your voice chat configuration, depending on what software your server is running o,n this is usually stored at/plugins/voicechat/voicechat-server.properties
Add the new port to voicechat
With the port that you created before, add it to the configuration for your voice chat.