Try this https://www.youtube.com/watch?v=CJ6AZMk2cy0
See if it works. I saw it working in Mojave.
Some Apple Support on this https://support.apple.com/en-us/HT202860
There's this old process that might work too https://www.youtube.com/watch?v=TjxAgiNqkDM (see description os the video for complete command lines)
As you still have access to the account, you can also open terminal and type sudo passwd root
Type YOUR own password from your original admin user
You'll be asked for a new root password twice.
Then try to enable root user via terminal https://osxdaily.com/2015/02/19/enable-disable-root-command-line-mac/
Some Apple support on root user https://support.apple.com/en-us/HT204012
See if you can move from there with access to root.
Be aware root user owns everything so it allows evil in the system core. Once you do what you gotta do, disable it.
Hope some of this could be of help.