So it does seem you want to claim your free trial for Apple TV+
To claim your promotion please follow https://support.apple.com/en-us/HT210627 and if you are having any issues and or prompted to pay immediately, please review the terms and conditions below**
If you purchased a device before July 1, 2021 you would have been eligible for 1 free year of Apple TV.
You have 90 days to claim that promotion, If you missed it, you are no longer eligible.
If you purchased it after July 1, 2021 You would be eligible for 3 months of Apple TV + but you would still have to claim that promotion with in 90 days of the device activation date.
*****Please review the terms and conditions as it contains eligibility requirements ****https://www.apple.com/promo/pdf/EN_US_ATV+_Promo_TandCs.pdf
Hope this helps ;)