INSTALLATION: 


for [REPLACE] version: (4seater)
replace REGINA car files (".ytd" AND ".yft") with openIV in this directory:

Grand Theft Auto V\mods\update\x64\dlcpacks\patchday3ng\dlc.rpf\x64\levels\gta5\vehicles.rpf\ 
done. Spawn as:  sedans ->"Regina"

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for [ADD-ON] version: (2seater)

1.Copy "ds21" folder to :\Grand Theft Auto V\mods\update\x64\dlcpacks

2. Using OpenIV, go to: \Grand Theft Auto V\\mods\update\update.rpf\common\data — find the "dlclist.xml"
and add the following line:

<Item>dlcpacks:\ds21\</Item>

Done!

To spawn the car using the ADD-ON trainer: 
sport classic -> Citroen DS21