Open Davinci Resolve, go to Help->Deactivate License
If you have a card with license key, that key can be used on 2 different devices in the same time. If one is deactivated, it will not affect your device. Once he deactivate from his computer means that you have one license key left to activate it on another mac/pc.
Broadcast Video Engineer Colorist Certified DaVinci Resolve Trainer