how to turn off two factor authentication?

See Two-factor authentication for Apple ID https://support.apple.com/en-us/HT204915 and more specifically the section entitled Can I turn off two-factor authentication after I’ve turned it on? You can't turn it off unless you recently updated your account. In this case, you can unenroll within two weeks of enrollment.

If you are in the two-week period, "Just open your enrollment confirmation email and click the link to return to your previous security settings. Keep in mind, this makes your account less secure."