How to use 'attach' in Blue Prism to get the correct handle of an excel file without knowing the workbook name?

I'm trying to write the content of an excel file that I downloaded in a web app into a collection. Therefore I open the workbook and then use the 'attach' action with the handle as output (no input values). However, in the next step I cannot do anything using the handle as it throws errors saying that the handle is not correct. I've already tried 'Get worksheet as collection' and 'Get worksheet name'. The latter gave threw me the following error:

: Failed to get worksheet name: wrong index. (exception of HRESULT: 0x8002000B