How do I turn off two step authentication

You can't, unless it is less than 2 weeks since you signed up.

On your iPhone.....

Tap Settings > Tap Your Name at the top of the window > Tap Password & Security > Log in to iCloud > Two Factor Authentication

Check to see if an option to Turn Off appears. If not, you cannot turn Two Factor off

Hello ~ From the article you came from…

*If you're already using two-factor authentication with your Apple ID, you can't turn it off. If you updated to two-factor authentication inadvertently, you can turn it off within two weeks of enrollment. If you do, your account is less secure and you can't use features that require a higher level of security.

~Katana-San~

You cannot turn that off. It is a safety and anti-theft feature.