First, we can try to 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 there. Click More on the right side under Ring My Device, Lock My Device etc. Then click Unlock Device and when you do that, your screen will be unlocked. If that didn't work, then the only option to get into the tablet is factory-reset it. There is no other way to override the lock screen if the Samsung website 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. Even if you take it to Samsung, they will not be able to unlock it for you.
Follow the steps below to factory reset it (make sure you follow the steps below exactly or it will not work);
Turn off the tablet. If you can't turn off, then hold down Volume down and Power until it turns off and then immediately do the next step.
Press and hold down Volume Up and Power buttons at the same time. When it turns on, release the Power button but continue holding down Volume Up button.
Android system recovery will be loaded now (may take up to 2 minutes. Press Volume Up and Power if it shows No Command)
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 tablet.
After factory reset, you need to set up the tablet again (like a new tablet). If there is a backup made on Samsung or Google account, you will get your data back. If you are unable to reset it from there, then try to erase it from this site (make sure you erase this problem Tab and not any other devices) --> https://google.com/android/find
(Loginwith the same Google account you used on the Tab to erase it) If you have any difficulty on following the steps above, please let me know and I will walk you through it.