Since there is no possibility to perform a hard reset I recommend you to visit a local phone service shop. They should be able to flash the operating system using 3rd party tools. Of you can do it by yourself, but there is a big chance you'll render it bricked after the operation. The Volume UP + Power button won't work since recovery is not activate for this type.
The hard reset was possible for previous versions of the tablet, but the new ones don't have the hard reset feature enabled.