1. Download the Kodiak from where it was purchased. You should end up with a .zip file of the most recent version.
2. Open the .zip file and find the folder inside, titled "Quest_Kodiak_v1.5" (for example).
3. Move the"Quest_Kodiak_v1.5" folder to your "X-Plane 11/Aircraft/" folder.
4. Open X-Plane.
5. Load the Kodiak.
A dialog box should open and prompt you for a serial number. After entering it you should quit and re-open X-Plane, to ensure the Kodiak loads correctly the first time.