You can try to do that using your Google account. After several wrong attempts, a message will appear on the screen that stats : Forgot pattern? You should tap on that and log in with the GMail account. If this didn't helped you, try to hard reset the tablet. To be noticed that by doing this, you will wipe all your data from the device bringing it to the factory settings. To do that, you should have your tablet turned OFF first. Try pressing the Volume Up, Volume Down and Power buttons simultaneously until an Android logo appears on the screen. Also, a menu should appear. You can use the Power button in order to navigate through it and select Wipe data / Factory reset using Volume Up key. This should fix your problem.