Allow me to step in and clarify things out for you about importing data from QuickBooks Desktop to Online.
The importing process is irreversible. You need to manually delete those data and re-import them.
If your QBO subscription is still within 60 days after signing up, then you can delete your data and start over. This way, you'll be able to transfer 4 years worth of information instead of 20 years.
Sign in to QuickBooks Online.
Look at the URL in your browser's address bar. Delete everything after the last / and enter purgecompany. For example: Before: https://...qbo.intuit.com/app/homepage After: https://...qbo.intuit.com/app/purgecompany
Click Yes to confirm the deletion process.
Select Wipe data.
Once the process is finished, you can start your books from scratch.