How do I set an active value on select dropdown control programmatically?

To set the active value on a select dropdown control, you must bind a property to the value in the select component and change that bind property in the event call

@page "/dropdown"

<select class="form-control" value="@listdefault" @onchange="@OnSelect" style="width:150px">
    @foreach (var template in templates)
    {
<option value=@template>@template</option>
     }
</select>

<h5>@selectedString</h5>
<select class="form-control" value="@citydefault" @onchange="@OnSelectCity" style="width:150px">
       @foreach (var template in citytemplates)
        {
   <option value=@template>@template</option>
}
</select>
<h5>@selectedCity</h5>
<button class="btn btn-primary" @onclick="@Change">Change</button>

@code {
    List<string> templates = new List<string>() { "America", "China", "India", "Russia", "England" };
    List<string> citytemplates = new List<string>();
    List<string> usa = new List<string>() { "Los-Angeles", "Florida", "Newyork", "Washington", "California" };
    List<string> china = new List<string>() { "Wuhan", "Beijing", "Shanghai", "Macau", "Taipei " };
    List<string> india = new List<string>() { "New-Delhi", "Mumbai", "Chennai", "Bangalore", "Hyderabad" };
    List<string> russia = new List<string>() { "Moscow", "Saint Petersburg", "Novosibirsk", "Yekaterinburg", "Kazan" };
    List<string> england = new List<string>() { "Birmingham", "Cambridge", "Manchester", "Leicester", "London" };
    string selectedString = "";
    string selectedCity = "";
    string listdefault = "India";
    string citydefault = "Mumbai";
    void OnSelect(ChangeEventArgs e)
    {
        if (e.Value.ToString() == "America")
        {
            citytemplates = usa;
        }
        else if (e.Value.ToString() == "China")
        {
            citytemplates = china;
        }
        else if (e.Value.ToString() == "India")
        {
            citytemplates = india;
        }
        else if (e.Value.ToString() == "Russia")
        {
            citytemplates = russia;
        }
        else
        {
            citytemplates = england;
        }
        selectedString = "Selected Country is: " + e.Value.ToString();

        StateHasChanged();
        Console.WriteLine("It is definitely: " + selectedString);
    }
    void OnSelectCity(ChangeEventArgs e)
    {
        selectedCity = "Selected CIty is: " + e.Value.ToString();
        Console.WriteLine("It is definitely: " + selectedString);
    }
    void Change(MouseEventArgs args)
    {
        listdefault = "Russia";
    }
    protected override void OnInitialized()
    {
        citytemplates = india;
        citydefault = "Chennai";
        base.OnInitialized();
    }
}

In the above sample, the city dropdown is changed based on the country selected in the country dropdown.