Flash Question: Debian on QNAP

[Patrick Leibach <tigerleibach@web.de>]

Hey Martin,

I have a QNAP TS-212 and successfully flashed Debian to the md3 and md5
to install Debian. I've been using it now, since a while and also
upgraded to Buster.
Now I'd like to fall back on Stretch while installing everything from
the scratch.
I tried to follow your instructions on
http://www.cyrius.com/debian/kirkwood/qnap/ts-219/install/ but
unfortunately the shell scricpt only works in QNAP firmware.
How can I change the script, that it works from Debian
or
How can I manually flash the initd and kernel to the flashblock3 and 5

Thanks for your help
Patrick