I have just realized that I have the wrong Social Insurance Number for one of my employees. How do I edit that and then how do I amend the t-4 issued ?

Hi lawsonspaulm,

Welcome to Community!  It's great to hear that you've selected QuickBooks Online Payroll to ensure your employees are paid on time.  Having the option to edit their information can be done seamlessly.  I'll be happy to assist!

Here's how to edit employee information;

1. Open Payroll from the left menu and then Employees

2. Click on the Employee name

3. Select the Edit ✎ in the What are [employees name] tax withholdings section 

4. Make the necessary corrections on the TD1 form

With regards to amending the T4 slips, this can be done directly on the CRA website.

Feel free mark this as solved for others who may experience the same issue.  Your success is important and we love to help!