to get a list of files on your device.
You may need to add some options if you want the tar archive is zipped (compressed).
Replace the "t" with an "x" and then add the files you want to extract at the end to restore your files.
You can use wildcards, but I suggest you put them inside single quotes, so that the shell doesn't do wildcard expansion before passing the parameters to tar.
tar -xvf /dev/st0 '*.txt'