1) Create yourself your own Admin account on your DEP Mac device.
2) Download the DEP Reset Script. Get the script from here: https://eucse.com/resources/DEPReset.sh
3) Amend the script to include the username of your Hidden Admin, and the user account name you use when setting up your DEP user.
4) run sudo chmod +x DEPReset.sh
5) run sudo ./DEPReset.sh
Ignore any errors you see, and then restart your machine.