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If you do not remember the Apple ID Password then follow the steps given in this Apple Article -> If you forgot your Apple ID password - Apple Support

If you do not remember the Apple ID then follow the steps given in this Apple Article -> If you forgot your Apple ID - Apple Support

If you are the owner or the owner has shared all information with you then to open Activation Lock:- If it is Activation locked, read here --> Turn off Activation Lock - Apple Support Activation Lock for iPhone, iPad, and iPod touch - Apple Support

Learn how to remove a device from a previous owner's account.

If you are not the owner and do not have the Apple ID and Password then there is no way that you can get into this iPhone unless the original owner shares the Apple ID and password with you. If you are lucky you can get into this iPhone if they (owner) accidentally remove the device from their Apple ID.

If you can't unlock your Apple ID

If you use security questions with your Apple ID, or if you don't have access to a trusted device or phone number, go to iforgot.apple.com. Then you can unlock your account with your existing password or reset your password.

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What if I can't access a trusted device or didn't receive a verification code?

If you're signing in and don’t have a trusted device handy that can display verification codes, you can have a code sent to your trusted phone number via text message or an automated phone call instead. Click Didn't Get a Code on the sign in screen and choose to send a code to your trusted phone number. You can also get a code directly from Settings on a trusted device. Learn how to get a verification code.

If you use iOS 11.3 or later on your iPhone, you might not need to enter a verification code. In some cases, your trusted phone number can be automatically verified in the background on your iPhone. It’s one less thing to do, and your account is still protected with two-factor authentication.

If I can't sign in, how do I regain access to my account?

If you can’t sign in, access a trusted device, reset your password, or receive verification codes, you can request account recovery to regain access to your account. Account recovery is an automatic process designed to get you back in to your account as quickly as possible while denying access to anyone who might be pretending to be you. It might take a few days—or longer—depending on what specific account information you can provide to verify your identity.

Do I still need to remember any security questions?

No. With two-factor authentication, you don't need to remember any security questions. We verify your identity exclusively using your password and verification codes sent to your trusted devices and phone numbers. When you enroll in two-factor authentication, we keep your old security questions on file for two weeks in case you need to return your account to its previous security settings. After that, they're deleted.

Can Apple Support help me regain access to my account?

Apple Support can answer your questions about the account recovery process, but can't verify your identity or expedite the process in any way.