How can I get data in blazor based on dropdown value

Hello.
I'm in the process of developing a blazor program. The page contains a drop down list, a button and a table. 
I need to select a client from the drop down list to retrieve the data for the client from the Database. 
But when I press the button, all clients come from the database in the table. I enclose the codes below.
Is there anyone can help me with that?

@page "/Kontoplan"


@using BOGF.Models
@using Gateway


<h1>Kontoplan</h1>

<EditForm Model="@klient">
    <div>
        <InputSelect @bind-Value="KlientId" name="KlientId" id="KlientId" class="form-control" style="width: auto; float: right">
            <option selected disabled ="">-- Vælg en Klient --</option>
            @foreach (var klient in klienter)
            {
                <option id="@klient.Id" name="@klient.Name">@klient.Id- @klient.Name</option>
            }
        </InputSelect>
        <button type="submit" class="btn btn-primary" style="width:100px; float:right" @onclick="@OnInitializedKontoplan">Hent</button>
    </div>
    @if (kontoplans is null)
    {
        <div class="spinner"></div>
    }
    else
    {
        <table class="table table-striped">
            <thead>
                <tr>
                    <th style="width:110px">LåsKonto</th>
                    <th>Kontonummer</th>
                    <th>Navn</th>
                    <th>Type</th>
                    <th>Moms</th>
                    <th>LockKonto</th>
                    <th>KlientId</th>
                </tr>
            </thead>
            <tbody>
                @foreach (var kontoplan in kontoplans)
                {
                    string lockkonto = kontoplan.LockKonto.ToString();
                    if (lockkonto == "Locked")
                    {
                <tr style="background-color:skyblue">
                    <td><input type="checkbox" checked /></td>
                    <td>@kontoplan.Kontonummer</td>
                    <td>@kontoplan.Navn</td>
                    <td>@kontoplan.Type</td>
                    <td>@kontoplan.Moms</td>
                    <td>@kontoplan.LockKonto</td>
                    <td>@kontoplan.KlientId</td>
                </tr>
                    }
                    else
                    {
            <tr>
                <td><input type="checkbox" /></td>
                <td>@kontoplan.Kontonummer</td>
                <td>@kontoplan.Navn</td>
                <td>@kontoplan.Type</td>
                <td>@kontoplan.Moms</td>
                <td>@kontoplan.LockKonto</td>
                <td>@kontoplan.KlientId</td>
            </tr>
                    }
                }
            </tbody>
        </table>
    }
</EditForm>

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

    [Parameter]
    public int KlientId { get; set; }

    List<KontoplanModel> kontoplans = null;
    KlientGateway gateway = new KlientGateway();
    List<KlientModel> klienter = new List<KlientModel>();
    KlientModel klient = new KlientModel();
    KontoplanModel kpm = new KontoplanModel();


    protected override void OnInitialized()
    {
        klienter = gateway.GetAllKlient();
    }

    protected void OnInitializedKontoplan()
    {
        kontoplans = gateway.GetKontoplan(KlientId);
        KlientId = kpm.KlientId;
    }

public class KlientGateway
    {
        ApplicationDbContext _db = new ApplicationDbContext();

        public List<KlientModel>GetAllKlient()
        {
            return _db.Klient.ToList();
        }

        public List<KontoplanModel> GetKontoplan(int KlientId)
        {
            return _db.Kontoplan.ToList();
        }
    }

namespace BOGF.Models
{
    [Keyless]
    public class KontoplanModel
    {
        public int Kontonummer { get; set; }
        public string Navn { get; set; }
        public string Type { get; set; }
        public string Moms { get; set; }
        public string LockKonto { get; set; }
        public int KlientId { get; set; }
    }
}