Hi @Eugene Pieterse, I wanted to make sure you're able to get back up and running.

I'll share how you're able to convert your client's company data from QuickBooks Desktop to QuickBooks Online seamlessly.

You're on the right track, a working trial version of QBDT is needed when converting company data from an unsupported year version. Yes, the link included in the article showing the restoration tool is not yet available. For now, we'll have to move your data manually by creating a CSV file.

Kindly read and use this article to learn more about the conversion and for the instruction: Why Can’t I Move Data from QuickBooks Desktop to QuickBooks Online?

Now that you're about to start working on the online version, here's a reference to learn more about the features and functions of QuickBooks Online. You can log in to any of our supported browser versions and use this reference for guidance: Help Articles in QuickBooks Online. 

It'll always be my pleasure to help if you have any other concerns besides converting company data in QuickBooks. Please let me know by clicking the Reply button and leaving a comment below. Don't forget to include my name, @JonpriL, and take care always, @Eugene Pieterse!