Hi,
I think what you need is the GetFile processor and not FetchFile. In the Fetch File you have to specify the exact file path and name that you want to fetch and you can't use wild card. However in the Get File you specify the path in the "Input Directory" then you can use Regex in the "File Filter" property to capture files with certain pattern. In your case the search pattern in Regex will be something like ".*xyz.*\.txt"
You need to watch for other Properties like "Keep Source File" which decide what to do with the file after its picked up. If you want to loop indefinitely then "False" would be the right value. Once the file is picked up you can save it somewhere else using PutFile processor. The "Recurse Subdirectories" let you decide wither you want to search root folder only or all folder levels.
If that helps please accept solution.
Thanks