My grandson has put a pattern lock on his tablet & has forgotten it. When I try to turn it off or sign in I keep being asked for the pattern I’m just locked out
You might keep trying patterns if you think that after a number of wrong patterns you could get right one but android will setup a timer to wait if wrong pattern is drawn and each time timer to wait will increase.
The next option would be a hard reset your device.
Please keep in mind
• Resetting your device will completely erase all user data on the device.
• After reset you may be asked to sign in with the previous Google account (as a security feature named FRP) that the device had previously signed in before Resetting. So, make sure you have sign in detials of that account.
How to hard reset Samsung tablet A ?
Switch off the device.
Press and hold the Volume Up key + Home key + Power key simultaneously.
Release keys when the Samsung Galaxy Tab screen displays.
Recovery menu would take a little time to appear(It would take couple of seconds to show you System Update so wait.)
Choose wipe data/factory reset by pressing volume - button.
Press power to confirm factory reset(choose delete all user data.)
It would take couple time to reset it, after process is done the option may appear to 'Reboot' device or it may be Rebooted to system automatically.
Now you would be asked to set up your tablet and you all screen lock is disabled.