how to shut off two-step verification

Do you really mean the old security method, "two step"?

Two-step verification for Apple ID; click here --> Two-step verification for Apple ID - Apple Support

See the section "How do I turn off two-step verification?

If instead you mean the current two factor authentication, two-factor authentication is enabled by default on new Apple IDs and cannot be turned off. If you have an old account and recently activated Two Factor Authentication note this section of an Apple support article:

"Two-factor authentication for Apple ID" --> Two-factor authentication for Apple ID - Apple Support

--> "Can I turn off two-factor authentication after I’ve turned it on?

... If you recently updated your account, you can unenroll within two weeks of enrollment. Just open your enrollment confirmation email and click the link to return to your previous security settings ..."

Here's a similar reply but with more up to date references to the article as it stands now:

Read the document: "Two-factor authentication for Apple ID" - Two-factor authentication for Apple ID - Apple Support

Two-factor authentication is enabled by default on new Apple IDs and cannot be turned off.

"If you're already using two-factor authentication with your Apple ID, you can't turn it off."

If you have an old account (several years old) and recently activated Two Factor Authentication note this section of the Apple support article -->

"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."