Are you talking about the NHL.tv app/website? If so, it's really chaotic there, and if you start a replay from the home screen, there is no option to select a broadcast. Not before you launch the replay, and not afterwards, either. (One of many deficiencies of the app/service, especially the missing "Watch game from the start" option, without spoilers, if the game is already in progress and not yet completed.)
However, in the iPad NHL.tv app, and in the browser on the web, too, if you first go to the Schedule screen (instead of the home screen), and then navigate to the replay you want and tap/click on it, it will give you the option to select the broadcast. (It gives me both the Rangers and the Islanders feed for the game you want.)