Wpf object binding? page transition

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VB

I hav a prob, i have this xaml code in MainWindow

<pageTransitions:PageTransition x:Name="pageTransition" Margin="5" TransitionType="Fade" Grid.Row="2"/>

and on other xaml, vbcode (to trigger page transition)

Dim admin As New Admin

            PageTransition.ShowPage(admin)


        End Sub

but it says Reference to a non-shared member requires an object reference

i need to target the pagetransition which is at MainWindow to update the page to navigate. but how can i do it? please help. thanks