Yes, you can manually enter the transactions for the Q3 on the 941 forms, EdOr.
I've got some information on how to enter these items in QuickBooks Online.
You can create liability checks for the third quarter and ensure to fill in the correct information however, we'll have to make sure that the Year-To-Date data are correct. That said, you can do a payroll liability adjustment.
I'd also recommend reaching out to your accountant so you'll be guided in doing the adjustment.
I've added this article as your guide about the adjustment process: Adjust payroll liabilities in QuickBooks Desktop.
Afterwards, you can run a payroll liability balance report to ensure that the data entered are correct.
Keep me posted if ever you need help in doing the adjustment. Have a good one!