Error Message Loop in 'Preparing' stage

Hello,

I am about to sell my 2019 Dell XPS 15 7590 Laptop, and so I followed the Microsoft instructions to reset the machine, (ie. Wipe it), before selling it.

I have somehow reached a stage in that process where I am being presented with an error message telling me to restart the computer and then restart installation of Windows, but each time I click OK to attempt to do that the machine restarts back to exactly the same screen with the same error message. See photo of the screen below, and note the above the word 'Preparing' is a rotating circle of blobs.

Can anyone advise me how to exit this loop please?