How do I default the Digi One SP unit to return it to DHCP configuration?

Realport
2

Here you go:

How to factory reset a PortServer TS or Digi One SP

3

To factory default the Digi One SP you will need to press and continue to hold in the hardware reset button located on the bottom of the unit. While you continue to hold in the reset button power cycle the SP. Don’t release the reset button until you see a flash code of 1-5-1 on the power led indicating that the has successfully returned to factory setting.