Thanks for posting in the Community! I've got you the steps to cancel your QuickBooks Online subscription.
Open a web browser on your computer, not a mobile device.
Sign in to QuickBooks Online.
Select Settings ⚙ and then Account and settings.
Go to the Billing & Subscription tab.
In the QuickBooks section, select Cancel subscription.
Follow the onscreen steps.
If you don't have a Billing and Subscription option it means that you bought QuickBooks Online through a mobile app store. You can check on this article for more detailed steps on how to cancel a subscription purchased through an app store.
Feel free to drop a comment below if you have any other questions. I'll be around to help.