How do I disable 2 factor authentication

See the "Can I turn off two-factor authentication after I’ve turned it on?" section in:

Two-factor authentication for Apple ID - Apple Support

Check your junk mail, it isn't an email for updating your device, when you turn on 2-factor authorization (and you have to do this unless your employer mandates and controls it) you do receive a confirmation email.

If it has been more than 2 weeks you can't. If it is less than that find the link in the email you received when it was activated and use it to cancel it.