Choose a car in game. Click tuning/customize, and "create dir".
Find the created folder in: Steam\steamapps\common\rFactor 2\UserData\player\Settings\AE86_Club\*Name of the car*
Paste the dds file there, and choose it on tuning/customize in game
Find the created folder in: Steam\steamapps\common\rFactor 2\UserData\player\Settings\AE86_Club\*Name of the car*
Paste the dds file there, and choose it on tuning/customize in game