Fill in what you can — it opens WhatsApp with your message ready to send.
Make / Model / Year — on your vehicle registration card, or the maker's plate inside the driver's door.
Chassis No. (VIN) — optional, but it pins down the exact part variant. Find it on your registration card or the maker's plate inside the driver's door.
No app? It opens WhatsApp Web instead. Your message is pre-typed — you tap send.