I was offered 3 months free trial with my new computer purchase, but when I go to sign up it only offers me 7 days free

1. Be sure to redeem the offer on your new eligible Apple device, not on a different device.
2. For Macs, be sure to sign in to the TV app (menu Account), or the redeem offer button may not be shown.
3. Verify that this is your first time redeeming for this service: one offer per user or family.

Read here how to redeem: Apple TV+ offer - Apple

Read here about the conditions: Apple TV+ offer - Terms and conditions - Apple

Read here if you have trouble redeeming: If you can't redeem your promotion for an Apple subscription - Apple Support

↳ Step 5 says to contact Apple Support for assistance if the previous steps didn’t resolve it.

Hi there!

You can check this link for more information on how to redeem the AppleTv+ promo: https://offers.appletvapp.apple/tvp01213mf

Also, please note that the Offer must be claimed in the Apple TV app within 3 months after first setting up your new device.

Hope that helps! Best of luck!

How do I get 3 months free trail