Where to add licencse Key? I instlld Prmium Plugin but does not recognize.

Where to add licencse Key? I instlld Prmium Plugin but does not recognize. Everywhere I go it says to buy the premium plugin to use features, but I did buy the premium version and that is what I have installed. I have tried redownloading the premium plugin and installing again but no change. I cannot find anywhere to enter a license key or connected it.