BMW E30 DTM skin for the RD premium driver academy.
Extract the rar file to a temporary location. Make sure it extracts the folder too. You should have a folder named RD_Drivers_Academy with all the skin files inside. Copy this folder to: X:\Steam\steamapps\common\assettocorsa\content\cars\bmw_m3_e30_dtm\skins\ and it should work.
Note: I have NOT tested this with other versions of the BMW E30
RaceDepartment Premium Driver Academy Skin 1.0
BMW E30 DTM Driver Academy