Welcome, and thank you for choosing QuickBooks Online, beanlogan!
I'm happy to explain why you can't pass through entering your employees' prior payroll data.
The reason why you're unable to proceed is the 0 tax declaration. I know you haven't had tax calculations in the previous software, but QuickBooks thinks that it isn't right since you paid your employees. QuickBooks only calculates the future taxes, and you can only proceed to once you enter the correct previous data.
What I can suggest is to work with your accountant to figure out the tax amounts of the previous payrolls. You can also use our paycheck calculator to get those figures. Please note that you may get a different net pay amount because of the taxes.
I've included some useful resources to guide you through setting up your payroll. Please check this out: QuickBooks Online Payroll Full Service Hub.
Feel free to reach out if you have additional payroll concerns, or anything related to QuickBooks.
Stay safe, and enjoy the rest of the day!