Bear in mind that whatever you do will probably only work for your specific router, changing to mine will probably mean your app will need changing.
Keep a reference to the process you start, and you can use Sendkeys:
Dim h As IntPtr = theProcessIJustStarted.MainWindowHandle
SetForegroundWindow(h)
SendKeys.SendWait("MyUserName{TAB}MyPassword{ENTER}")
or similar.