How to link Razer Kraken V2 actication code (don't have it) to Synapse 4?

Hey there! So, I’ve been using Synapse 2 for a long time now, as well as my Razer Kraken V2 Pro 7.1. Since Synapse 2 will be discontinued, and I still want to be able to configure my headset with legit software, I need to know where to find the activation code. Since it’s been bought in 2019, the box is long gone. If I’m not mistaken, when I linked it to Synapse 2, I did input the serial number there,  but I see no option to export it or link it from Synapse 2 to Synapse 4. The Synapse 4 software only identifies my mouse (Deathadder Elite). 

Thanks!