As below, there does not appear to be a Goodmans model that relates to the one you have posted about.
I can't offer specific advice, but I'd suggest trying to get to the main menu and select "factory reset" or "first time installation" and go from there. Unplugging the power and leaving for ten minutes before powering up again may clear a software glitch potentially causing your problem. As far as I'm aware, there is no password needed for this type of reset. It would be interesting if you could post a reply on how you solved this issue if you manage to do so.

Rupert
May 2020

Goodmans or Goodwin's?

Can't find ANY reference to Goodwin's or any model SDDTR.

This may help:

https://www.goodmans.co.uk/support/freeviewdtr.html

Phdsr
May 2020