WPF Combobox have no ClickItem

Good day everybody,

I try to use a ClickItem in WPF-Combobox but unfortunatly there is no ClickItem Method.

Look:

That is my Combobox: 

Aliases.JTL_Wawi.HwndSource_Window2.KundeNeueAdress.NeueLayoutGroup.CompanySelect

Photo 0.jpg , 1.jpg

TC make one Object for every Item in Combobox!

Photo 2.jpg

Have you maybe a solution. I want to use ItemIndex but there is no Itemindex Method