[EpiData-list] Unique key in EpiData Manager for Mac?

Hello all,

I recently download EpiDataManager and -Client for Mac. I'm now recoding all my files in terms of valuelabel settings, checks and, most importantly for me now, unique keys. How can I do this? There is no solution button-wise and I cannot find a solution coding it into the .epx file

Hope there's someone out there who can help me!