How to edit a PHRASE? (Help needed) - Very simple

[koolfire]

Hi,

I installed a hack from where people can invite other users to the forum

I searched for the phrase used in the email and here's whats inside

Hello there,

You have been invited to join the {1}!
 
To sign up please visit the following page:
{2}/register.php

This invitation was sent to you by forum member {3}.

All the best,
{1}

How do I add a referrerid={USER ID OF THE INVITER} to this phrase? What's the {phrasethingy} for this? I want to add it after register.php so all the registrations are tracked to the referer

Please help
Thanks!