I understand you wanted to delete a vehicle in QuickBooks Online (QBO). However, we don't have an option to remove a vehicle by default. I can provide you with alternate steps to make your vehicle inactive.
Here's how:
Go to the Expenses menu. Select Mileage.
Click the drop-down arrow next to Add trip. Then, select Manage vehicles.
Look for the vehicle you want to make inactive.
Select Vehicle no longer in use. This brings your vehicle to the Inactive section of your Manage vehicle field.
If you need to reactivate a vehicle, you can follow the same steps. Then select Activate.