With the NVR added to Hik-Connect:
- Select the camera to live view
- Click the 2 way audio icon (microphone)
Depending on firmware the 2 way audio may start automatically (this seems to be a recent change, possibly in the latest Hik-Connect app, which means less clicks to get to the function). If however a prompt appears with 'Device' and 'Channel' options, select 'Channel' and the two way audio will start.