connect tmobile to apple tv

You need to Follow T-Mobile's steps to connect your T-Mobile account to your Apple ID. It should automatically replace the regular Apple TV+ subscription when you do that.

https://www.t-mobile.com/tv-streaming/apple-tv-plus-deal#Redeem

I am an Apple TV+ customer and I pay monthly through Apple. How will Apple TV+ On Us work for me?

Once you redeem the Apple TV+ On Us promotion, your paid Apple TV+ subscription will pause and Apple TV+ On Us through T-Mobile will take over. Once the T-Mobile offer period is over (if applicable), pay $6.99 per month. Cancel anytime.

The password is your Apple ID password.

If you forgot your Apple ID password - Apple Support

I forgot my password for Apple TV w T-Mobile