First I don't know why anyone would switch from the superior downloaded version to the pricy online one voluntarily. And I doubt you will be able to transfer the file at all .... but you will have to ask in the QB forum or contact intuit directly ...https://forums.quickbooksusers.com/forum/quickbooks-software-support/quickbooks-pro-forum
@Critter My guess would be that the user is worried about not being able to use Windows 7 for the 2019 tax return with the desktop software and is changing to the online software to avoid upgrading his computer to Windows 10 or whatever.
@jp5825 What kind of Business return do you file? Do you buy the Turbo Tax Business program or Home&Business? There is no online version of the separate Business program. Business is only a Desktop program for Windows computers.
The online version equivalent to Home & Business is called the Self Employed version. H&B and Self Employed versions are only for personal 1040 returns that need schedule C for self employment/Sole Proprietor/Independent Contractor etc.