Once you have installed the trial version of Enfold, you do not need to install it again. You just need to activate your license with the serial number Strata provided when you made your purchase.
You will need to open Illustrator, and then go to the Help menu > Strata Enfold 3D CX > Trials and Licenses. This will open the EskoArtwork Plug-ins dialog. Click "EskoArtwork License Manager" in the lower left corner.
That will give you a window where you can "Activate" your license. Select the trial version, and then click Activate. This takes you to Esko's website where you can register the serial number ("product key").
You will need the email and password you originally used to activate the trial version to complete this process on Esko's website.