Revest stores the backup settings and the machine information in your (%appdata%\Genie9\Revest) folder. When you move to a new machine, change the hard drive, reinstall Windows or even uninstall Revest without selecting the option to Keep Revest Settings (Recommended if you wish to reinstall), then these information will be deleted.
Now, when you reinstall Revest and sign in to your account, if you have already reached the maximum number of computers*, you will be asked to delete or archive the older machines in order to be able to add the new machine.
The good news is that Revest has a De-Duplication feature that will prevent uploading the same previously backed up files again. For more information, please refer to this article.