How do I watch the new Carpool Karaoke the seri...

Hi my name is Guy and I have a problem.

How do I watch the new apple program 'Carpool Karaoke The Series' on iTunes, I have the apple music but when I press the link in the apple website it says that I have to select the apple music in preferences, and I don't know how to do that.

How do I select the apple music tab? ( I am on a mac )