At start up, press the power button and the volume UP button at the same time, then release at the same time. The recovery menu should appear when you release the buttons. Sometimes it can be a little finicky. Try to make sure you're pressing the buttons exactly at the same time. I think it can work as well if you press the volume UP button first, and then the power button immediately after, holding both down at the same time, then releasing.
From the recovery menu you can restore the tablet to new, then reset a new password. You will have to reload all your apps and all existing data will be erased.