In the case of an iLok license, all you need to do is redeem the license and activate it to your preferred location. This will either be your computer, cloud, or iLok USB Key (2 or 3).
You do not need to install the plugin again, as the full version is already installed. The trial license can simply expire and iLok will switch over to the perpetual license automatically.
For more info see here - https://joeysturgistones.com/pages/ilok-instructions