Years ago, I purchased the PoE Definitive Edition from gog. The Definitive Edition included White March I and II. My recollection is that during the install, I was given the option to install WM I and II and I declined because I wanted to experience the original game. On my launch screen the icons on the lower right are grayed out.

I now want to install WM I and II. If I click on the grayed out icons it takes me to Paradox's website to purchase the expansions but I already own them as part of the Definitive Edition from gog.

How can I now install WM I and II? Do I have to completely uninstall POE and reinstall and selected the expansions on the reinstall or is there an alternative?

Just download the DLC's from your game library page, install and the game will see them. Hope this helps.

When I go to my Library, it only shows POE Definitive Edition. The DLCs are not listed separately since they were not purchased separately.

In comparison if I look at Battle Brothers in my Library where I did purchase the DLCs separately I do have links for four separate "DLC Installers".

In hindsight, I probably should have installed the DLCs when prompted and simply deactivated them until I was ready. I am simply trying to avoid and uninstall/reinstall. Any other suggestions?

Actually I am mistaken. I own the Hero Edition not the Definitive Edition so I don't have the DLCs. I will simply purchase them now.

Glad you've got to the bottom of the issue - enjoy the expansions :)