Answered question
How to Modify the current phone number to a different new phone number after the Fizz plan is actived?
René D have the best best answer.
But if you you want to port a new number, you have to buy a new sim card.
Other answers
Go to your account
My Plan
Manage
Change this phone number
Chizz :))
My question is how to change the phone number linked to the actual phone plan
Sorry I don't think understand your question.
The only phone number you get to link to your account is the one active with Fizz.
.
Earlier answer was to show you how to change your Fizz number.
Chizz :))
You can't port a new number after it's activated. You can only do as Rene said, change to a new number from fizz pool.