Disable two step authentication

See the following from Two-factor authentication for Apple ID - Apple Support

If you already use two-factor authentication, you can no longer turn it off. Certain features in the latest versions of iOS and macOS require this extra level of security, which is designed to protect your information. If you recently updated your account, you can unenroll for two weeks. 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 and means that you can't use features that require higher security.

2 Step Verification or 2 Factor Authentication?

2 Step Verification 

How do I turn off two-step verification?

Sign in to your Apple ID account page.

In the Security section, Click Edit.

Click Turn Off two-step verification.

Create new security questions and verify your date of birth.

You'll get an email confirming that two-step verification for your Apple ID is off.

Apple ID - Two Step Verifications FAQ