Restore default Debian system

[perceg]

It's pretty simple! Download the latest build of the default Debian image, flash to an SD card, boot from the SD card, and let it flash to the eMMC.

would one use an iso burner to transfer the download to the sd card  ?

No. You need to use a raw image burner tool. Balena Etcher, Win32DiskImager, or normal old "dd" would all do the task.

How does one flash it to the eMMC?

Lets say you used "Etcher" to write the latest debian image to the SD.

Then you booted from the SD.
You will need copy that Debian Image to the SD or Download it again.

Open a new terminal on the same folder than the Debian "zipped" file is located.

Use the next command to "extract" the image file.

• unxz pinebookpro-debian-desktop-mrfixit-190905.img.xz
  

That is going to extract the .img file and remove the original file. (this process takes a couple of minutes).

Then to write that image to the eMMC run the next command:

• sudo dd if=pinebookpro-debian-desktop-mrfixit-190905.img of=/dev/mmcblk1 status=progress
  

You will be able to see the progress of this process.
At the end, turn off your Pinebook Pro, remove the SD.
Turn on the Pinebook again.
Done.

That's exactly what we were looking for - thank you!!