Open the Settings app
Tap Device Options
Tap Reset to Factory Defaults
Tap Reset to confirm
Wait for the device to restart and erase all data
If the tablet is frozen, press and hold the Power button for 40 seconds
After it restarts, repeat the factory reset steps from Settings
If you cannot access Settings, boot into recovery mode if supported by your model
Select Wipe data/factory reset in recovery
Confirm the reset
Wait for the reset to complete and the device to reboot