You are not providing much information, which is probably why you are not getting much help. Posting what you have done so far would make things much clearer.
But in the meantime, I presume that your file search is running some sort of loop, maybe one folder at a time. At the end of each pass add the file count from that folder to files processed so far, and calculate progress. To do that you need to know the total number of files that will need to be processed. Unless you can work that out very quickly you will need to have that information already prepared, maybe by doing a file scan when the app starts, or saving information from a previous run.
You say that you want to update a text editor with the progress information. Maybe you mean an EditText (although a Label would be more usual) but if not then, again, provide more information.