Are you referring to a company file from QBO and wants to open using QuickBooks Desktop? If so, you can try using a QuickBooks Desktop trial version so you can convert to or from QuickBooks Online. Let me help route you to this link: QuickBooks Desktop trial.
You'll need to save the backup file on your computer hard drive so you can restore the company file once you're done installing the QB trial version. Please check out this article for the detailed steps: Restore a backup company file.
However, if you're referring to something else, please let me know. I'll be here to help however I can. Have a good one.