VBA index match to to fill textbox form combo?

Hello to all!
I want a textbox to be populated from a combobox value. This works fine as long as my data are on the same workbook. I did population with an indexmatch formula.
My data are currently in another workbook (workbookname=Data).
Could somebody help me to refer to it in the below indexmatch code? i mean where exactly to put the workbook after the index..
Thank you very much in advance!

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I tried to refer to it before the sheet1 but it does not work...
Anybody help please?