Please visit the Chaos Downloads Page where you can find builds for all our products.
Select your product and then select the version you wish to use. Click on the "Download" button and run the installer.
In order to see older versions, click "Go to other versions" on the Chaos Downloads page, and then "View older versions".
For example if you are using Maya version 2019 you need to download a build for V-Ray for Maya version 2019 as otherwise your license will not start properly.