Invoke a Method of Child form opened with Using Statement

I am trying to figure out how to invoke a method of a child form which is opened in a using block.

In my code, I have a MainForm which is a MDI parent. MDI parent holds a reference of parent form . A parent form where the below method is declared.

1. The ParentForm Instance is available in MDIParent form as shown in the following code.

   MainForm.cs

    private void OpenParentForm()
    {
        try
        {
   
            FormParent frmParent = null;
            frmParent = Application.OpenForms["frmParent"] as FormParent;
   
            if (frmParent != null)
            {
                frmParent.Focus();
            }
            else
            {
                frmParent = new FormParent();
                frmParent.Name = "frmParent";
                frmParent.MdiParent = this;
                frmParent.Show();
            }
   
        }
        catch { }
    }
   

2. The Child form is opened in

   frmParent.cs

    private void ShowChildForm()
    {
        try
        {
            using (ChildForm frmChild = new ChildForm())
            {
   
                if (frmChild.ShowDialog() == DialogResult.OK)
                    this.RefreshData();
   
                frmChild.Dispose();
            }
        }
        catch { }
    }
   

The ChildForm having following method.

ChildForm.cs

private void ChildMethod()
{
    //........
    //........
    //........
}

Following is my InvokeMethod

ReflectionHelper.cs

public static async Task<bool> InvokeMethod(Form Window, string methodName, object param)
{
    try
    {
        Form mainWindow = Window;
        var MainWindowtype = mainWindow.GetType();
        MethodInfo MethodtoInvoke = MainWindowtype.GetMethod(methodName, BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Instance);
        if (MethodtoInvoke != null)
        {
            ParameterInfo[] pars = MethodtoInvoke.GetParameters();
            object[] Parameter = null;

            try
            {
                object returnValue = null;
                if (pars != null && pars.Length > 0)
                {
                    Parameter = new object[pars.Length];
                    foreach (var item in pars)
                    {
                        int index = item.Position;
                        if (param != null)
                        {
                            if (param.GetType() == item.ParameterType || item.ParameterType == typeof(object))
                            {
                                Parameter[index] = param;
                            }
                        }
                    }
                    returnValue = MethodtoInvoke.Invoke(mainWindow, Parameter);
                  
                }
                else
                    returnValue = MethodtoInvoke.Invoke(mainWindow, null);
            }
            catch (Exception ex)
            {
                MessageBox.Show("Exception InvokeMethod  \n" + ex.Message);
            }
        }
    }
    catch (Exception ex)
    {
        return false;
    }
    return true;
}

Currently, I am able to invoke Parentform instance methods which are available in MainForm.

Helper.cs

public class Helper
{
    private async void OpenParentForm()
    {
        ReflectionHelper.InvokeMethod(static Instance of MainForm, MethodName, null);
    }
}

I want to invoke MainForm>>frmParent>>[Instance of ChildForm in using block of frmParent.cs].ChildMethod()