First you should download the mod from the owner of the mod :
https://www.gtainside.com/en/gta5/cars/104144-toyota-8pralift-add-on-livery-template/

Then Install My livery designs with OPENIV :

Mods>update>X64>dlcpacks>8pralift>dlc.rpf>x64>8pralift_vehicles.rpf>8pralift.ytd

Follow this info and then open edit mode

After that open 8pralift.ytd click import button and choose my liveries.