Use OpenIV to open dlc.rpf files of your addon, extract .yft and .ytd files and you can use them as replace. But to make car work good and don't have bugged textures or bad handling as rolling out use lines from vehicles.meta and handling.meta to replace lines of replaced car. (if you change dashboard line in vehicles.meta dont forget go to the end of file and replace child and parents lines of that vehicle too, if you don't do it your game would crash at loading).
If you want change plates, colors, lights intense and used tuning files (delete them or use another .rpf as default) you have to edit carvariations.meta too and for tuning parts is using file carcols.meta
I wasn't learning from tutorial, but there is lot of tutorials for using mods. I think you would find some tutorial how to use addon as replace on this site.