C#

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace FindcboBox
{
	public partial class Form1 : Form
	{
		public ComboBox mycbox;
		public Form1()
		{
			InitializeComponent();
			{
				Cbo1.Items.Clear();
				Cbo1.Items.Add("een");
				Cbo1.Items.Add("twee");
			}
		}

		private void Button1_Click(object sender, EventArgs e)
		{
			GetcboBox("Cbo1");
			GetcboBox("Cbo2");
			GetcboBox("Cbo3");
		}

		private void GetcboBox(string cbName)
		{

			mycbox = new ComboBox();
			foreach (Control mycbox in this.Controls)
			{
				if (mycbox is ComboBox & mycbox.Name == cbName)
				{
					MessageBox.Show("hallo");

					mycbox.Text = "kl";
					mycbox.Items.Add("een");					
				}
			}
		}
	}