I got a year free Apple TV with my phone

Every Apple ID account needs a valid payment method (or ‘None’). If you select ‘None’, then you can only pay for items using account balance (from bank transfer or gift card).

Payment methods that you can use with your Apple ID - Apple Support

If your payment method is declined in the App Store or iTunes Store - Apple Support

Change, add, or remove Apple ID payment methods - Apple Support

What you can buy with your Apple ID balance - Apple Support

Add money to your Apple ID balance - Apple Support

Redeem your App Store & iTunes Gift Card - Apple Support

Check your Apple ID balance - Apple Support

Redeeming the free year offer for Apple TV+ will start a subscription. To start a subscription, you will need to have a payment method that can be charged automatically and periodically for the subscription fees. To start a subscription with payment method ‘None’, you will need at least the Apple ID account balance of one billing cycle ($4.99). It is the responsibility of the subscriber to have enough account balance on the next due day. Even the free year offer will need a payment method for the time after that year, if you are still subscribed by then.

If your payment method is declined or unusable, or if you owe money to Apple, then your access to the iTunes Store and App Store is revoked until that dispute is settled. Contact Apple Support to sort this out.

If none of your payment methods can be charged, your last order will remain unpaid. View your purchase history to see your recent purchases and find out which order is unpaid.

We can’t look into your account. Contact Support if you need assistance with this

A valid payment method is required to set up the tv plus subscription

on your phone, in settings- Your name - Media and purchases , is where you can manage this.