To do this, you will have to visit the profile of the person who brought you to E.
If you view the profile of a member with an id less than yours, and you do not have a referrer set already, you will see:
"Did I bring you to Elliquiy? Click here!"
Which will take you to a page to either confirm the referral, ignore it, or set 'no referrer' as necessary.
In order to prevent hijinks, about 5,000 members who referenced Google or another search engine in their introductory post had their referrer set to 'no referrer' by script. This may have clobbered a few members unjustly - please send me a PM if you want me to manually set your referrer to someone (note you will need to have mentioned them in your intro thread).