Did not know that FIZZ do not work with iphone 5 what should i do

Iphone 5 is not compatible. You can see the devices that are compatible here: https://fizz.ca/en/faq/compatible-devices

Hi,

The iPhone 5 isn't compatible due to the limitations in software updates available on the device. You won't be able to update your iOs to the latest versions which are required to work on the Fizz network.

https://fizz.ca/en/faq/compatible-devices

Since "Only iPhone 5s models, or more recent, are compatible with the Fizz mobile network." Is there a way to force the carrier when the phone is already updated (no update available) ?

While it is not officially supported... it does work with a little extra configuration :)
I recommend you take a look at this: https://bit.ly/2Qpox3D if you go over to Reddit we will be able to help you.

@ Emre Y. : Merci! Le iPhone 5c qui n'est pas, officiellement, supporté, fonctionne maintenant.

@Hélène C. Bienvenue! :)

Bonsoir, @Emre Y. j'ai un iPhone 5C déverrouillé, et j'ai installé l'APN que vous suggéré. Malheureusement, je n'ai toujours pas accès à internet. merci de vos aides.

Try installing this APN profile instead (open link with Safari):

https://github.com/Manouchehri/Fizz-APN/raw/master/Fizz.mobileconfig

Thank you Jeffrey, it is working for me now (Iphone 5)!