If you ever need to recreate admin account on your Mac, this is the quickest and safest way to do it without breaking your Mac:
- Boot into Single User Mode by pressing ⌘ + S before you hear the Apple chime.
- Mount the drive by typing /sbin/mount –uw / then ↩ enter.
- Remove the Apple Setup Done file by typing rm -v /var/db/.AppleSetupDone then ↩ enter.
- Reboot by typing reboot then ↩ enter.
- Complete the setup process, creating a new admin account.
This will force macOS to redo the initial first account creation, and doing so will not affect the current user profiles (they will remain intact) – so, if you prefer to make them as admin later, you can do that as well by logging in using the newly created admin account, then go to System Preferences, then Users & Groups, select the existing user, and tick “Allow user to administer this computer.”
I tested on macOS 10.14 Mojave and it worked:
ark:db andy$ pwd /var/db ark:db andy$ ls -al .AppleSetupDone -r-------- 1 root wheel 0 Apr 4 2017 .AppleSetupDone ark:db andy$ uname -a Darwin ark.local 18.0.0 Darwin Kernel Version 18.0.0: Wed Aug 22 20:13:40 PDT 2018; root:xnu-4903.201.2~1/RELEASE_X86_64 x86_64 ark:db andy$
If you have any questions or comments, please feel free to post down below. Cheers!