how to change phone number?

I think you better contact fizz bye the chat to do that. You can use that link to have the chat bubble.
https://fizz.ca/fr/faq/plaintes

you can go to facebook of fizz and send a message !

I think this link will answer your question : https://fizz.ca/en/faq/how-do-i-get-a-new-phone-number

Mannage Plan and < Change this phone number >
https://zone.fizz.ca/dce/customer-ui-prod/#/account/plan/...

you can do it in your account

@Johanne M. No need to contact Fizz to change the phone number. @M.T. @MoYe B. and @Audrey B. all have the right answer.