@Susan - Sober Peer 

Just to clarify, do you need to migrate a whole data or some portion of data from QB Desktop to QB Online? If your QBO account is > 60 days older, you are unable to purge it anymore and should purchase a new account.

https:// quickbooks.grsm.io/US
https:// quickbooks.grsm.io/us-promo

Another option, utilize a migration tool. i.e TPExporter for Desktop, TPImporter for Online

https:// transactionpro.grsm.io/qbo