Hi and welcome to the forum.
I had a 2004 Starcraft and the manual was as useless as the one that came with my 2020 Cougar. First, does everything else 12 volt work? If the slide is the only thing not working, you need to check the fuse. It is behind a plastic panel that needs to be pressed in at the top for the door to open. That panel is your converter and power center. It will be low and have a plastic frame around it. When it opens you will see a bank of breakers and another of fuses. If you are lucky the fuses will be marked. Best to check the fuses with a meter as not all blown fuses are obvious. Sorry but I do not remember where the manual override access is but a look under the open slide will give you a good idea of where the access is. I do remember ours was a rack and pinion setup and they are usually easy to access. Also, see if it works plugged into shore power.
Keep us posted.