Hey @ENkay1
You need to actually get the File Item ID to update the properties of that file. It is a unique integer that is generated by SP itself when the item/file is created. You are not creating the file in this flow which means you will first have to get the file and then reference the ID of the file in the Update Action.
So in this case, if you have the filename that will be unique and the details of that in the Excel too, you can get all files and add a filter query to filter by the name of the file and then use that ID to finally update the properties.
For later on, Maybe have the ID of the file stored in the Excel column (maybe a Flow that creates an excel row when a file is cretaed and saves it ID in a coulmn over there).
BTW, Current item that you have referenced in the ID is basically the item that you are iterating on in the apply to each loop.
Hope this Helps!
If this reply has answered your question or solved your issue, please mark this question as answered. Answered questions helps users in the future who may have the same issue or question quickly find a resolution via search. If you liked my response, please consider giving it a thumbs up. THANKS!