The steps to reset QuickBooks Online will depend if you're using the app or accessing your account using a browser. Know that this process refreshes QBO and deletes the stored data on the app, or browser which causes problems in the program.
Here are the steps that you'll need to perform.
For QuickBooks Online app:
Click Help on the navigation bar at the top.
Select Reset App Data.
Allow a moment for the process to complete, and then close the app.
Be sure to right-click the app and Run as Administrator when re-opening.
For the account that is accessed on the browser, you'll need to clear its cache so the gathered files will be removed. They are often the main reason for the unusual behavior in QBO.
I'm also sharing here some great resources about utilizing QuickBooks and managing the app: