When the HIT is active, still up on Mturk - look on the top left that says (HIT Details) in blue font. Click on that. There should be a popup that shows the HIT Details. On the bottom of that popup, there's a 'Contact This Requester' in blue font. Clicking on that will bring up the form you can fill out to write your message. If you have already done the HIT and want to contact them. Look in your dashboard. Click on the date you did it. There will be 'contact requester' on the right in blue font. HIT is not active or you've never done their HIT, you can go to Turkopticon (TO) and search for that particular requester by entering their name or requester ID. You have to have sign up for TO in order to see it. You can do the same with Turkerview. If all else fails and cannot find a way, you can always post in the forum and ask around. We are happy to help!