Hello there, @pierslangdon. I can share with you steps on how you can upload your QuickBooks Desktop (QBDT) file to QuickBooks Online (QBO).
In uploading or converting your QBDT file to your QBO account, you'll have to use the program itself. Since you no longer have the QBDT software, you can download and install a trial version to restore the file and start the conversion process from there.
If your QBDT file version is too old compare to the available trial version (QBDT 2022) of the program, you may reach out to our technical support team to help you get the correct trial version.
Once everything is set, you're now ready to upload your QBD file to QBO. After the conversion, review if everything in the company file is working properly. You can check out this article for reference: What to expect when you switch from QuickBooks Desktop to QuickBooks Online.
I've also attached this link for additional information about converting your account from QBDT to QBO: Learn about converting from QuickBooks Desktop to QuickBooks Online.
In case you'll need helpful links and guides to assist you in doing QuickBooks tasks, you can visit our QuickBooks Help page. From there, you'll find a number of help articles and even video tutorials based on the QuickBooks feature you've searched. You can also bookmark them in your browser for easy access and use them as your future reference.
You can always post your file conversion concerns here in the Community. I'd be glad to help you out again. Have a good one.
