<EditForm Model="@selectedCar" Context="formContext">
    <DataAnnotationsValidator />
    <ValidationSummary />

    ....My <InputText>'s for all values I have in my object

    <button type="submit" @onclick="@(() => SaveCar(formContext))">Save</button>
    <button type="submit" @onclick="@(() => UpdateStockQuantity(formContext))">Update stock quantity</button>
    <button type="submit" @onclick="@(() => DeleteCar(formContext))">Delete</button>
</EditForm>

@code {
    [Parameter]
    public string Id { get; set; }

    CarModel selectedCar;

    protected override async Task OnInitializedAsync()
    {
        selectedCar = await _CarService.GetCar(int.Parse(Id));
    }

    protected async Task SaveCar(EditContext formContext)
    {
        bool formIsValid = formContext.Validate();
        if (formIsValid == false)
            return;

        selectedCar.Id = await _CarService.SaveCar(selectedCar);
    }

     protected async Task DeleteObject(EditContext formContext)
    {
        selectedCar.Id = await _CarService.DeleteCar(selectedCar);
    }   

    // ... plus same approach with UpdateStockQuantity.
}