Hi there. Sometimes it's necessary to switch from QuickBooks Online to Desktop. I see that Fiat Lux - ASIA has shared some helpful info on the third-party apps you can use to migrate your data. While there isn't a direct way to convert your data, you can take advantage of the third-party migration apps which can be found on our app store using this link here. Another option would be manually exporting your data out of QuickBooks Online and importing it into QuickBooks Desktop. I encourage you to check out this helpful article with more info on how to: Export Data out of QuickBooks Online. I recommend you also check this article that shows you how to Import and export data in QuickBooks Desktop. Since you'll be starting with QuickBooks Desktop, here's an article that guides you in 

Getting started with QuickBooks Desktop.

Give this a try and let me know if you have questions. I'm here to assist.