How to use voice chat wotks in project?

4.15 version, I use this model [OnlineSubsystem]
DefaultPlatformService = Null, to achieve the LAN interaction, in this mode below to achieve voice chat? If i can, I did not find the relevant documents or tutorials, can send the link address to me? I made the necessary set in Config, but I did not find any blue chart in any Voice Chat related nodes, I should be how to do in the blueprint, thank you!