If you go to eBay motors using a desktop browser and follow the link in the upper left under My Garage where it says "Find Parts for My Vehicle", you should wind up here:
https://www.ebay.com/g/mygarage
From there, you should be able to select "Delete Vehicle". If that does not work for you, try another browser.
It is also possible to delete a vehicle using the eBay app; select the vehicle from your garage on the main page, and then use the three dot menu to reveal a delete option. At least that is how it works on the Android version.
