Just unzip the file and insert the complete folder to your STEAM folder like this:
C:\Program Files (x86)\Steam\SteamApps\common\assettocorsa\content\ cars\bmw_m3_gt2\skins
At the Assetto car menu inside the game take the BMW M3 GT2 and change the car design to the Monster Energy™ one
All rights reserved. Names, trademarks and copyrights are property of their respective owners.
BMW M3 GT2 "Monster Energy" 1.0
BMW M3 GT2 Monster Energy™