Below are the steps to remove a user's PIN administratively so that you can sign into their email account without a required PIN being sent to their device.

    1. Log in to Google Admin with an administrator's account.
    2. Click on Users.
    3. Click on the user. 
    4. Click on the Security section, and then click on the 2-step verification section.
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    5. Click on Off and then click the Save button.
    6. You should now be able to sign in to the user's email account without the two-step verification PIN and make your changes.