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Is the phone completely frozen and not responding to touch ? Or is it not allowing you unlock it using finger print ?
If it is completely frozen and not responding to touch, then hold down the Volume Down and Power button at the same time for 10-15 seconds or until it restarts itself. When it restart, release the buttons and let it load. Then see if it is working.
If it is still not allowing you to login to the phone, then enter some wrong passcode for multiple times, it should ask for the Gmail account associated with it. So use that Gmail account to reset the code.
If that didn't work, then we can unlock it directly from Samsung Find My Mobile service. This will only work if you have the Find My Mobile option enabled on it. Go to this website --> https://findmymobile.samsung.com/
Login to your Samsung account. Select your device on the left and click Screen Unlock at left column. This will unlock the screen and reset the finger print and password.
If that didn't work, then the only option to get in to the phone is factory-reset it. There is no other way to override the passcode screen if the Gmail or Samsung unlock option didn't work. Factory reset will erase everything from it and return it to new (like Out of Box). This is how they designed the device. Follow the steps below to factory reset it;
Turn off the phone
Press and hold down Volume Up, Home and Power buttons at the same time.
When it turns on, release the Power button but continue holding down Volume Up and Home button.
Android system recovery will be loaded now
Select wipe data/factory reset. (Volume buttons to go up or down, select with Power button)
Select Yes — delete all user data.(Volume buttons to go up or down, select with Power button)
Then select reboot system now(Volume buttons to go up or down, select with Power button)
That should factory reset the phone. Then do the initial setup and it will be unlocked. Please let me know if that didn't work, so we can continue troubleshooting.
If you don't have any important files on the phone, then you can reset the phone using the above instructions.
If it is completely frozen, then hold down Volume Down and Power for 10-15 seconds and it will force restart.