Use the menu Help->Serial Numbers… window to add serial numbers that you own. Type in a serial number and click ‘Set’ to add it. Repeat the process if you need to add multiple serial numbers. If accepted, the product name that you are adding will be added to the list in the window. Restart the program (not the computer.)
Font and Design collections will not need their serial numbers to be entered in this window. Once you have installed a Font, the program will ask for its serial number when you run the program. Enter the serial number at that time, and you will not be asked for it again after that.