How to write filenames with wildcards

Hi , I am totally new to sl and I having a hard time in writting dynamic filenames.

my file naming convention is - filename_xx_xxxxx.txt
and the file is in sl under the same branch.
So , Under file option in file reader ,
I am writting → filename__.txt
But I am getting the error that no such file exists.(Failure: Unable to read from)

Thanks for your help guys!