I found these instructions:
This device can be easy to hard reset, just follow these instructions to reset it.
Using Reset button: 1. Find the reset hole on the right bottom corner of the device and poke it with a paper clip or bobby pin for 5 sec.
2. The pattern should be gone after the reboot.
If that didn't worked you should try this hard reset combination:
1. Switch off the device.
2. Press and hold Volume Up and Power Button at the same time till you a menu.
3. On that menu, Highlight Wipe Data/Factory reset using volume down then press power button to select it.
4. On the next option select Yes using volume down and power button also.
5. After the reset, select Reboot system now using power button.