Can I amend a filed T4 summary that is incorrect

Hello pfaloon, 

Thanks for connecting with us here. It's vital you're able to amend your T4 and I'll be happy to point you towards the right path. 

In order to accomplish this goal you'll need to contact our support team using this link here. One of our specialized payroll agents will be happy to take a look at your T4 and help make the appropriate adjustments. 

In the meantime, check out this helpful resource regarding T4s in QB Online: How to prepare T4 slips and summary. Feel free to keep me posted on how you make out. I'll be here to assist.