Reinstalled Transmission plugin - username "transmission" missing

[Ed the Penguin]

Hi all,

Firstly.. new to FreeNAS and fairly new to Linux/Unix systems. I can just about navigate around the system and vi or nano files!
I reinstalled the Transmission PBI file after previously removing it. Since then, I don't seem to have the user ID transmission for the permissions anymore.

What is the best way to reconfigure this user?

Thanks!