Thanks for getting in contact. There are a couple of different ways to download and install this content depending on the platform this was purchased on. For games purchased or activated directly from our Ubisoft webstore or Uplay client then you should be able to download and update this contend directly from the Uplay client. You can find further details regarding this here.
If this was purchased through Steam, Epic Games or any other 3rd party game store you may need to check with them directly regarding the installation of this product but if you require any further assistance, please feel free to let us know.