Download the troubleshooter from here https://support.microsoft.com/en-au/help/17588/fix-problems-that-block-programs-from-being-installed-or-removed
Execute the download as an administrator and click on next.
You can choose whether installing or uninstalling the program. We strongly recommend uninstalling to erase all the registry keys that are preventing the clean setup of the new version of the same program.
You can choose any of the Bizagi programs, in this case, Modeler which is the one with the register key issue.
Once the uninstall is finished, you can launch the Modeler setup.exe again to fix the problem.