i have an iphone 4 that i use as an ipod and it is on IOS 7.1.2 and cannot be updated. how to get past two factor authentication

You turn it off for the Apple ID, not the device. To enter the code, if you see a password box, enter the password (ABC) followed by the code (123) or ABC123 (no spaces).

From the article below updated on 24 Apr 2020. 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.       

As Eric stated, you cannot turn it off. But you can log in on an iPhone 4 by using the following instructions from Two-factor authentication for Apple ID - Apple Support

If you use two-factor authentication with devices running older OS versions—like an Apple TV (2nd or 3rd generation)—you might be asked to add your six-digit verification code to the end of your password when signing in. Get your verification code from a trusted device running iOS 9 and later or OS X El Capitan and later, or have it sent to your trusted phone number. Then type your password followed by the six-digit verification code directly into the password field.