Replacing Ubuntu OS with Android OS Is there a straightforward step-by-step instruction to replace Ubuntu OS with Google OS on a BQ Aquaris M10 HD tablet.

I know nothing about computer code and nothing can be assumed. These instructions need to be precise. I.e. do I need another computer to perform this operation If so, what kind? If it can be done entirely on the tablet, then exactly how is this done?
Short answer: No

I don't know your tablet, but a straightforward instruction will not be available. Your tablet is also provided with Android, so there exist the working android port. Normally the producer of the tablet don't provide the needed files to re-flash the device.
Normally the image is build on a development computer and the image is flashed on the device. To replace your OS another computer will be needed (if you have the needed files)
Technically it's possible to create a USB memory stick that update your OS without interaction, but that's normally not provided by the producer of a "consumer tablet"

(sorry for my bad english, hope you understand my message)