Follow these few steps to install Twinmotion content pack.

Step 1: Download the asset package at the bottom of this article.

Step 2: Unpack downloaded file anywhere you like on your harddrive

Step 3: Open the explorer at C:\Users\Uername\Documents\Twinmotion\UserLibrary and copy the unpacked asset package to this location.

Step 4: Launch Twinmotion

Step 5: Check if the added content is now added to the User Library. 

and you use it at your own risk