Sorry for bothering but I cannot find it even there - it only gives a download link just as before. 
Hi, in that case you do need to find the mail we sent on Thursday, or your original purchase mail, from when you bought the game. Alternatively you can request a new purchase mail from this page: https://itch.io/docs/buying/already-bought
All of these mails contain a link to the page where you can redeem your key.