How to add a Microsoft Excel add-in
If you want to add an additional Excel add-in, you have to copy the file to the AddIns folder on your computer.
Write %appdata% into the Windows searchbox on your startmenu and press "ENTER".
Navigate to the Subfolder Microsoft\AddIns
and copy the new add-in file into this folder
Now start Excel and navigate to "Datei" -> "Optionen"
then "Add-Ins" and press the button "Gehe zu..."
The new add-in (which was copied in the first step) should appear in this list. Select it and press the "OK" button.
Now there will be a new menu option "Add-Ins" displayed in Excel, choose it and the add-in is now available for using.