Restore\Maximize another application

In my application I am checking to see if another instance is already running. If so, I pop up a message box saying so. Instead, I would like to restore\maximize the original application from the task bar, but not sure how to do so.

this is how i accomplished this, check to see if it works for you:

VB Code:

Declare Function ShowWindow Lib "user32" (ByVal hWnd As Int32, ByVal nCmdShow As Int32) As Int32
 
        Dim proc() As Process
        proc = Process.GetProcessesByName(Application.ProductName)
        If proc.Length > 1 Then
 
            If proc(1).Id = Process.GetCurrentProcess.Id Then
                ShowWindow(proc(0).MainWindowHandle.ToInt32, 9)
                Microsoft.VisualBasic.AppActivate(proc(0).Id)
 
            Else
                ShowWindow(proc(1).MainWindowHandle.ToInt32, 9)
                Microsoft.VisualBasic.AppActivate(proc(1).Id)
            End If
            Exit Sub
        End If