Open the downloaded dlc.rpf with an archive program like 7zip or Winrar (I think Winrar supports it too). You can then navigate through the folders and find all the files you need (meta and ytd files).
Move ytd files to a folder called stream, meta files anywhere inside the resource, define your __resource.lua as mentioned in the tutorial you said and you’re done.
It’s very easy, don’t overcomplicate it.
More detailed, see Simple tutorial on how to add vehicles to your FiveM server [Add-on/Replace] Part II