Can’t unlock your Android device
If you can’t unlock your Android phone or tablet, you can erase your device, set it up again, and set a new screen lock.


If you can’t sign in to your Google Account, follow these steps.

Erase your device
Important: These options will erase all data stored on your device, like your apps, photos, and music. Data backed up to your Google Account can be restored later.

Option 1: Reset your device from another device
You can erase your locked device using a computer, or another phone or tablet. To erase this way, the locked device must:


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Be turned on.
Be connected to the internet.
Have Find My Device turned on.
Learn how to remotely erase an Android device.

Option 2: Reset your device with its buttons
You can erase your locked device using its power and volume buttons. To learn how to reset your specific device this way, visit your manufacturer’s support site.

Reset your pattern (Android 4.4 or lower only)
If your locked device is running Android 4.4 or lower and has a pattern-type screen lock, you can use your Google Account to reset your pattern.

After you’ve tried to unlock your device multiple times, you’ll see “Forgot pattern.” Tap Forgot pattern.
Enter the Google Account username and password you previously added to your device.
Reset your screen lock. Learn how to set a screen lock.

Source>>
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If you want to unlock your phone with gmail account. Than follow steps that are given below:
Enter your gmail username.
Enter password.
Choose option send one time password to your gmail.
Enter otp in particular place.
Your phone will get open.

Or if you not have your gmail with you than perform steps below to unlock phone:
Enter alternate email that connected with gmail already.
Enter OTP.
Put otp on particular place.
You will get in into your system.