I bought an "open box" tablet from ebay. The Operating system has been upgraded to OS7, from OS6. I need to go back to OS6, in order to be able to use my SD card to hold my apps. Can anyone guide me on this? The only WIndows programs that I find, Such as android studio do a lot more, and the only link to the OS6 that I've found on google says that it is just for their own products. Thank you.