Hello there, Nathan_Pearce.
Let me share details about converting payroll information from QuickBooks Desktop (QBDT) to QuickBooks Online (QBO). This way, you'll be able to determine how to record your employee's YTD.
When you convert a company file from QBDT to a new QBO company, it includes your employee's information but not your payroll data. QBO imports the current year's paycheck information as lump sums. Since it's not converted, you’ll have to enter the past YTD payroll info for each employee.
Seeing that you've already processed your first payroll for this year using QuickBooks Online Payroll, I'd recommend contacting our Payroll Support team. They have the tool to enter your employee's YTD information in your account.
To learn more about things you'll need to do to start managing your business using QBO, kindly refer to this article: Getting started with QuickBooks Online. It contains related articles that'll guide you on what to perform after moving to the program.
Please let me know if you have other concerns. I'm just around to help.