You can restore a file from tape yourself using the RESTORE command (be sure you
know how to use the tape drive), or you can use the PUMPKIN command to queue a
request with the Great Pumpkin, who comes by night to restore your files.  This
will get your file back in a day or two, usually.

Both of these commands run the DART program.  The syntax of the commands is

  RESTORE  {<dest>←}{<source>}
  PUMPKIN  {<dest>←}{<source>}

where the "{" and "}" delimit optional text, <source> is the name of the file on
tape to be restored, and <dest> is the name of the file on disk to be written.
(It will be the same as <source> if not specified.)

For more information, see Appendix A5 of the Monitor Command Manual, available
online as the file MONCOM.BH[S,DOC] with updates in MONCOM.UPD[S,DOC].