disney+ existing subscription

I have an existing Disney + subscription direct and I want to download the app to watch my Disney + on my Apple TV. I can find the app but it’s asking me for my Apple login to open it not my Disney + account. All the articles I have read just say download and login but there is no download and use existing subscription option?

Any advice I don’t want to log in for a free trial which then results in a 2nd subscription to pay?

ian