deactivation

I bought a new Mac last year. I forgot to deactivate on my old one. That leads to this notification when I tried to activate my Key on current device : "This license has reached its activation limit and can no longer be used to activate new product copies" please help me to DEACTIVATE on my old...

I had to restore my previous laptop to factory default and now I am trying to install on a new machine. But I am unable to do so as the license is still active on the previous machine. I couldn't find a way to deactivate on the web. Please advise the process for deactivation