Hi, I am trying to remember, as it’s been a long time and I no longer have Android on my Teclast (I broke it but the Windows 10 still runs well ?.
I believe it is a either a combination of volume + power or housing down the power button for longer than usual – it should give you a graphic bootloader type screen offering one system or the other.
I’ll check later when I charge my Teclast, although u broke the system the loader still works ?.
Follow up to my previous message; I have successfully brought up the start up screen. I held down volume + and power buttons until I saw the device was starting.
If I remember correctly the options at the top left of the screen allow you to specify the default system. The two main buttons in the centre of the screen are for immediate start-up selection