If you have a "stairs retraction defeat switch" near the door, try toggling it. It may need to be reset. Other than that, start the search for fuses and breakers, including the chassis breakers, because the steps are powered by the chassis battery (as you have discovered?).
2018 (2017 Sprinter Cab Chassis) Navion24V + 2016 Wrangler JKU (sold @ ????) - 2016 Sunstar 26HE (sold @ 4600 miles) - 2002 Roadtrek C190P (sold @ 315,000kms)