I understand you must uninstall Corel 2020 first on your old machine, before you can install it on a new one. But suppose your old computer has crashed and it won't reboot. Probably the reason a lot of people go out an buy a new one. How can you install Corel 2020 on your new machine if you can't uninstall it on your old one?
If you log into your Corel account online, you should be able to look at Product Status and Subscriptions to see your active installations.
Find your "dead computer" installation there, check the box beside the computer's name, and use Remove selected machines.