Where to find key?

Hello, this may be a stupid question, but I bought this program a few years ago and was looking to install it on my new computer, but I forgot where to access my activation key. I checked my humble bundle purchases, but I could not find anything. If anyone could help me out with this, I would be grateful. It may also be helpful to say that I have already redeemed the key twice, so if that is the maximum amount then that may be the reason. Thanks!