How do I cancel my apple tv on my roku tv?

Or on third party devices with the Apple TV app: Manage subscriptions in the Apple TV app - Apple Support

Use an internet browser on any computer to cancel as described below from How to cancel Apple TV+ - Apple Support

How to cancel Apple TV+

1. Go to tv.apple.com.
2. Choose the account icon  at the top of the page. (If you don't see the account icon, tap or click Sign in, then sign in with your Apple ID.)
3. Choose Settings.
4. Scroll to Subscriptions and choose Manage.
5. Choose Cancel Subscription.

I want to cancel my subscription to Apple TV

Ghaa22 wrote:

I want to cancel my subscription to Apple TV

The information has already been provided. Follow the steps by FoxFifth.