Hi there, @Advanced_User.

You'll have the option to log in to QuickBooks Online (QBO) during the conversion process. From there, you can select your existing QBO account.

For step-by-step instruction, please check out this article: Move your QuickBooks Desktop file to QuickBooks Online.

I'm also sharing this article to guide you in using QBO: Get Started With QuickBooks Online.

Reach out to me again if you have follow-up questions or concerns about the QuickBooks migration. I'll be around for you. Take care and have a great day ahead.