the slide runs on battery power, not shore power.
do you not have a battery on the trailer?
didn't the dealer show how to manually retract the slide, in case of no power?
you also might try hooking up the trailer to the tow vehicle and try to bring it in.
of course, you'll probably still need the battery installed.
and Zoe the Wonder Dog(R.I.P.)
'07 Roo 23SS pushing an '07 Chevy Avalanche
Equalizer WDH and Prodigy BC