Head over to the official Uncertain website and wait for the pop-up.
The fields are in Russian, in the top one you need to enter your name, and in the bottom one your e-mail.
When the email comes, click on the “confirm subscription” and wait for the second mail with the Steam key.
My 1st email came at 9:20pm and the 2nd @ 8:35am (both went to junk folder)
Approximately how long is the wait for the pop-up?