Welcome to the Community,
... and installed ESXi and vSphere ...
For the Hypervisor (ESXi) you can register for a free license key at https://www.vmware.com/go/get-free-esxi .
However, in case you are evaluating a vSphere environment wih vCenter Server, go with the 60-day evaluation period (no keys required). Remember, that once assign a free Hypervisor license to a host, it cannot be managed in vCenter Server anymore!
let me know witch version you need ?
I have some License from some version of ESXI.