1. I created a new account using the link
https://eservices.cic.gc.ca/ols/login.do
2. Login to the created account
3. Click "Continue to Online Services"
4. Click "Request a refund" link
5. Select the following options:
Immigration, citizenship or a Canadian travel document for a non-Canadian
Online
I paid using IRCC’s payment service and attached a receipt to my online application
6. Click "Sign in" link at the bottom
7. Will show an option to enter Receipt number. Enter you receipt number and Search
8. Click "Request a refund" and enter the details request.
9. You will receive a notification email
Hope it helps... all the best