Setting APN on iPhone, How to!
There is no APN parameters you can set manually on iPhones.
To have an iPhone updating the carrier network, you need a internet connection.
Therefore, the first time you try to get the carrier update from Fizz, you might need to connect to internet trough a WiFi connection. so it can download the parameters package
this https://fizz.ca/en/faq/what-are-fizz-network-settings-apn procedure gives you steps to force the Fizz carrier update once you are connected to the internet trough WiFi.
Adding to this, going into the Settings / General / Information / on your iPhone, you should see on the Carrier line, Fizz 34.1; if not, some user reported that it does trgger the carrier update routine.
Then you just need to restart your iPhone and enjoy Fizz!