How to turn off two factor authentification

You don't.

It is now required for many features of iCloud. Once it's been activated for 14 days, it is impossible to turn it off.

Then it can't be turned off.

See here to learn how to use it:

Two-factor authentication for Apple ID - Apple Support

Use the link in the email you got when you enabled it to turn it off.

If you enabled it when you created the account, it can not be turned off at all.