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" - https://support.apple.com/HT204915
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"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 ..."
This is for a different security process but it is likely similar:
Two-step verification for Apple ID - https://support.apple.com/HT204152
Read the section about "How do I sign in to my account using an app that doesn't support entering two-step verification codes?"
Also: Jan 2017 Community Specialist sterling_r post: https://discussions.apple.com/message/31213055#message31213055 - "On older software, if you are not given a box to enter the verification code, you can simply put it immediately after your password. Note that this would not require a space."