Reset FreeBSD root user password:

Step # 1: Start FreeBSD server/workstation.

Step # 2: Press Enter key at boot loader.

At Welcome to FreeBSD! boot menu press spacebar key to pause default booting

Type number 2 key (type 2 number) to boot into single user mode

Next you will see the following prompt from system:
When prompted Enter full pathname of shell or RETURN for /bin/sh:

Press Enter key to boot into a single user mode. Next, you will be immediately dropped into a single user mode without a root password.

You need to remount / (root) file system in read and write mode with mount command, type the following commands:
Sometimes you must use fsck command and next press y->y->y

# mount -u /
# mount -a

Setup a new password with the passwd command for root user:
# passwd

Next type exit command to boot FreeBSD into multi-user mode environment:
# exit

OR You can just reboot the system:
# reboot