Access the link below to navigate to the My Listings section of your account. Then, click on the Rent tab. You should then see your listing along with the option to edit any of the rental listing information.
Let us know if you experience any problems accessing or updating your listing information. You can always give our Customer Service team a call at 888-466-3501 Monday - Friday 7am to 4pm PST, or send them an email via http://www.trulia.com/help/ask/
If its not attached to your account, find the listing and claim it. If its claimed by someone else, contact Trulia directly and report this.
Also, you can go to the top right to listings and add a listing.