I understand that you are looking for a way to remove the vehicle listed that you have never owned. I am here to share information regarding this.
In QuickBooks Self-Employed, if you don't use the vehicle anymore, you can make it inactive, so it doesn't show up on your list of active vehicles. However, the option to permanently remove it is unavailable at this time.
In your case, you may want to check and ensure that none of your existing trips stays linked to that vehicle. For more information, refer to this article: Set up vehicles and mileage tracking in QuickBooks Online to use with the mobile app.
I'm adding these articles you can use in the future:
If you have any further questions, please feel free to ask. Also, don't forget to check out the articles I provided for future reference on mileage tracking in QuickBooks Self-Employed. Best of luck with your business!