Thanks for joining the Community, william31.
Currently, there isn't a process to merge accounts. If you have two subscriptions and don't want to receive invoices for the one you're not using, it can be cancelled.
Here's how:
1. Log in as an admin user.
2. Go to your Gear (⚙) icon, then Account and Settings.
3. Open the Billing and subscription tab.
4. Click Cancel subscription or Cancel Online.
5. Hit Continue to Cancel.
6. Choose Submit and cancel subscription.
7. Select Got it.
I've also included a visual guide:
Now the subscription you chose to cancel will be discontinued.
I'm including a couple resources about using QuickBooks Online which may come in handy moving forward:
I'll be here to help if there's any other questions. Enjoy the rest of your day!