Connect with and learn from others in the QuickBooks Community.
Consider purchasing a 3rd party file migration service to QB Desktop file. You may open the converted file on the trial license of QB 2020 Pro and self migrate it later to QB Online.
You'd want to make sure that your QuickBooks is updated to the latest version. This way you can convert your company file into QuickBooks Online seamlessly.
You need not worry, you can export your lists such as vendors, customers, inventory, and chart of accounts from QuickBooks Simple Start. Then, import it in QuickBooks Online. You can read through these articles for more detailed steps in the importing process:
Let me know if you have other questions. I'm always here to help.