This was the answer I received from Trulia Customer Service:
1. Log into your own Trulia profile, then click on the "Find an Agent" link in the green search bar at the top.
2. Search by your agent’s name and service area.
3. When your agent appears in the results, click their name.
4. Select the “Reviews” tab beneath their name and photo on their profile page.
5. Select the orange “Write a Review” button.
6. Your old review and ratings will populate in a pop-up window. Here, you can make any corrections needed.
If you'd like it to be removed instead of edited, feel free to just edit the review to "Please delete this review, Trulia" and have them flag the review as spam.