Good morning, @mark307.
Congrats on making your first post here in the Community. Let's work together to get this problem handled.
If you're needing to move your whole QuickBooks Desktop file to QuickBooks Online, here's a guide that provides details and instructions on how to do so:
Move your QuickBooks Desktop file to QuickBooks Online
If you're just need to load a certain part of your data to QBO from QBDT, let us know and we'll help you further.
I hope the guide does the trick to get your data over. If you need me again, hit the Reply button below. I'll be waiting for your response!