In more detail : The data.hkl file

¹⁰ The file data.hkl is a free-format ASCII file containing h, k, l, F,$\sigma$(F) for your unknown (target) crystal structure. Use all data to the resolution limit you want to work at (eg. 4Å). Do not use all your data to, say, 2Å with a large protein, unless you have plenty of physical memory and a year of CPU time to spare. Alternatively, you can place all your data in the data.hkl file, and then run the program with something like Qs -reso 20 4 -auto 3, where the -reso 20 4 flag defines resolution limits. If you work with the CCP4 suite of programs, the program you need is mtz2various (but mtzdump will also do). Your file should look like this :

  -23   1   9      329.80      3.55
  -23   1  11      190.39      4.39
  .................................

Footnotes

...P¹⁰

If you have a .mtz file containing just h, k, l, F,$\sigma$(F), mtzdump is the easiest way to prepare the required file :
mtzdump hklin my.mtz > data.hkl
reso 20.0 4.0
nref 100000
go
Then, edit the file data.hkl with your favourite editor to remove the lines above and below the list of reflections.