How to turn off authentication code

2 Factor Authentication 

From the article below updated on 8 Nov 2019. If it has been on longer than 2 weeks, you can't turn it off. 

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

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, however, you can unenroll for a period of 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 a higher level of security.

Apple ID -Two-factor authentication

You would need to change your security type to remove that.

Here is a link for managing your Apple ID.

Note you may not be able to change that back to change that.

Manage Your Apple ID

Hope that helps