add reference library InteractionDefault.dll.

use this code below :

using Microsoft.Dynamics.Retail.Pos.Interaction

ManagerAccessForm formManager = new ManagerAccessForm();
var cekDialog = formManager.ShowDialog();
if (cekDialog == DialogResult.OK)
{
   // your logic
}

and dont forget to set ManagerAccessForm() to public on InteractionDefault project.

public ManagerAccessForm()
{
   InitializeComponent();
}