On the right side of the Airtime interface, click Webstreams tab, then click +New button.
In the pane on the right, fill in the information for the stream that you'd like to rebroadcast. Once finished press the Save button. You can now schedule that Webstream to any show in Airtime Pro. Once a show with a Webstream starts, Airtime Pro will connect to and rebroadcast the stream to your listeners. If you are rebroadcasting a stream from another Airtime Pro instance, the metadata for the airing tracks will automatically appear on your stream.
Read more about Webstreams here!