Here is how you can use the car which was unrealeased:
1. In TDU2VPE, check unrealeased button and uncheck all other boxes.
2. Open the Model tab, and choose the car which has closest dimensions to Bugatti.
3. Press Load.
4. Now, you have to rechange some files which you have downloaded:
4.1 Rename the files: body goes chiron.bnk; interior chiron_i.bnk; wheels chiron_f_01.bnk.
4.2 Put these files:
body: Euro -> bnk -> vehicules -> high
interior: Euro -> bnk -> vehicules -> interiors
wheels: Euro -> bnk -> vehicules -> rims -> bugatti
5. Go back to TDU2VPE, and go to Tires/Rims; press folder/file name. as folder, choose bugatti, and both rims should be chiron_f_01
6. Choose Miscellaneous tab; open sensitive data, file name definition; and rename to chiron.
7. Put the car in a dealership which you want, and press Apply.
this is very basic way to get the car into the game, keep in mind that you also need to change camera position, or even change the location wheels in zmod.