If you never paid for Resolve, uninstall Studio and install the free version from Blackmagic's website. If you did pay, use your key and delete the activation.dat file if it's stuck in a loop.

Davinci Resolve Keeps Asking For Activation Key Access

If you never paid for Resolve, uninstall Studio and install the free version from Blackmagic's website. If you did pay, use your key and delete the activation.dat file if it's stuck in a loop.