In the Distribution overview, you will find the option to send a reminder to individual people. This is different to the option to send reminders to whole groups of people (people who have not answered yet, for example). Once in Distribution overview, select Sent objects and click on the linked number. A pop-up window will then appear, showing a list of all participants. Locate the person you would like to send a reminder to and then click the e-mail icon next to their name.