Unable to input an older serial key - licensing server shut down?

I have an older serial key for Adobe CS3 and when I try to activate it with the install CD, I constantly get the same error of connection failed. I did some searching and found this:

https://community.adobe.com/t5/get-started/cs3-activation-the-solution/td-p/9343026

For step 3. the author says to key in the old serial to get a new one. Where is this place where you can key in an old serial to get a new one?