I mean I made an error and chose reimbursement, but it is actually a bonus so should have been compensation.
Okay, it will depend on what version of QB payroll you use and if you can edit paychecks on your own or submit changes to Intuit.
Presuming you use a version where you can control the paycheck
1. Open paycheck
2. View details - write down the net amount so you do not have to hunt for it
3. Unlock net pay (sometimes necessary,sometimes not)
4. Re-categorize the reimbursement as Cash Advance
5. verify net pay remained the same, save
Next pay
1. enter the bonus pay item
2. in deductions enter the cash advance repayment (I use two different items that each post to same account)
3. Save
Reminder, that if bonus pay is sizable (and presumably even if not) there is a mandatory flat rate FWT on the bonus pay.
If you use other than a DIY version then, armed with your calculations from above, call payroll support tpo have them edit the issued paycheck