Here are the steps to reset root password on FreeBSD 11.
Boot the system, and wait till you get to the Welcome to FreeBSD boot menu.
Once you are there, press 2 to boot the system to single user mode.
Wait till the server shows a following message: “When prompted Enter full path name of shell or RETURN for /bin/sh:”, and then press Enter key to complete the boot process to single user mode.
You will now be presented with console input.
In the console type following commands:
mount -u / mount -a
Now you can use
passwd command to change root user password, by typing in the new password when asked, and they retyping it on second prompt.
Once you have set a new password, reboot the server, and log in with the new password.