Download the JustStream Audio Driver Installer from the site, run it and follow the installation instructions as described in the screenshots below.

Onsite version of the app already comes with the JustStream Audio Driver Installer. To install the driver using it, while mirroring your screen press the Mute/Unmute button. 

You can download Audio Driver here.

 In the appeared Alert window, click the Install button to start the installation.

Next, you will need to follow the step-by-step installation instructions.

Note: You need to have administrative privileges to install this software.

To complete the installation you have to restart your Mac.