Hold Command-S when booting.

## Create New Admin Account
Apparently Apple closed this loophole [see here](https://eclecticlight.co/2019/09/25/is-single-user-mode-sum-dead/) as macs with a {T2} chip don't support Single User Mode. But [see here for more](http://www.theinstructional.com/guides/how-to-re-run-the-os-x-setup-assistant). Boot in single user mode (Command-S). Then at the command prompt type (the `# comments` don't need to be typed):
```
/sbin/fsck -fy # check drive for errors
/sbin/mount -uw /
rm /var/db/.AppleSetupDone
```
and the reboot. This is good for old macs.