it's vital all your payroll forms have the correct information to file with the government. QuickBooks Online Payroll is a great tool able to help you keep track of payroll done so that you can use the totals to generate your year-end forms like T4 and Releevé-1. I can point you in the right direction to edit that information.
In order to edit information on the T4, you can follow the steps in the Process T4s/RL-1s section of the linked article. There is also some other helpful information about the forms within the article.
If you have any other questions, feel free to reach out here.