Since this is an update release, it requires the base game (specifically the Dragon.Star.Varnir-CODEX release) to be previously installed. How to Use
Point it to your existing Dragon Star Varnir installation folder. Dragon.Star.Varnir.Update.v20200407-CODEX.rar
The "proper" (NFO) for the release details a minor update for the PC version of the game. Release Details Game Name: Dragon Star Varnir Update Version: v20200407 Group: CODEX Release Date: April 7, 2020 (as indicated by the filename). Update Notes (NFO Summary) Since this is an update release, it requires