Delete apple id
My ex-worker who used this phone with his ID signed in, later he quit and pass this phone to me, we need to delete his Apple ID and sign with mine.
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Apple can completely reset a device if a person can provide sufficient evidence of valid ownership. Do this online at: Activation Lock support request - https://al-support.apple.com/#/additional-support Apple says, "Proof of ownership documentation is required," but does not detail what currently constitutes proof. Prior to this new online service Apple typically required the original receipt issued by Apple or an Apple Authorized Reseller and documented provenance (so typically it would be the original owner who does this, or a descendant with legal proof of ownership). This will give you access to the device but won't restore access to the account used to lock it. There is nothing that can be done to expedite an Activation Lock request.
Apple recommends you "Keep your receipt after you buy an Apple device" --> Keep your receipt after you buy an Apple device - Apple Support
If this could possibly happen again in your company: "Learn how to manage Find My iPhone Activation Lock and Lost Mode on supervised devices with Mobile Device Management (MDM). This article is intended for system administrators at businesses and educational institutions." - Use MDM to manage Activation Lock and Lost Mode - Apple Support
https://www.apple.com/business/resources/docs/Managing_Devices_and_Corporate_Data_on_iOS.pdf
https://www.apple.com/business/site/docs/iOS_Deployment_Overview.pdf
Apple Configurator - Official Apple Support