I don't believe there is way to do so, but there is two methods of which you could attempt to figure it out.
Click on the application link again and click the "login with Steam" button and see which account comes up first. Chances are, you selected the one that came up (if it did). http://www.insurgency-sandstorm.com/closed-technical-alpha
Reach out to them and see if they can help you out. This is probably more ideal but it could take a while for them to respond. firstname.lastname@example.org
Hopefully you'll hear a response, best of luck.