You can record church tithes by creating a donor and item for the tithes within QuickBooks Online. Here's how:
Go to Sales on the left panel.
Select Customers tab.
Click New customer at the upper-right corner.
Enter the information of the donor. Then, hit Save.
Once done, create an item for the tithes by following the step below:
Follow the first step above.
Click Products and Services.
Click the New button, and select the Type.
Enter the information, and click Save and close.
Then, I'd recommend reaching out to your accountant when setting up an account for the items. This is to make sure everything will be properly recorded and ensure your reports are accurate.
Also, you may want to check these articles for additional references and tips when handling transactions in QuickBooks Online: