- Copy folder "petrosgr" to Grand Theft Auto V/Update/x64/dlcpacks/
- Go to /Update/update.rpf/common/data/dlclist.xml and open with notepad and paste this: 

<Item>dlcpacks:\petrosgr\</Item> 

- Go to /Update/update.rpf/common/data/extratitleupdatedata.meta open with notepad and paste this line: 

<Item type="SExtraTitleUpdateMount">
			<deviceName>dlc_petrosgr:/</deviceName>
			<path>update:/dlc_patch/petrosgr/</path>
		</Item> 


save and replace the old one.
- Done

if you want to remove the white livery just replace it with the one in the "No livery" folder.
Use any trainer and spawn by name "xsarawrc"