This can be accomplished using either the I/O TMPDIR or the run option -tmpdir. If you want to do it through I/O TMPDIR, you can do like in picture the attached picture "TMPDIR_IO.png", if you want to use run options, you can do it like in the attached picture "TMPDIR_RunOptions.png". There are also arguments for maximum allowed file size and network drives covered in the documentation on TMPDIR or Run Options if you need more info on that, I have linked the pages below.

In short, we can set maximum file size using filesize={filesize in GB} and for network locations we can set slow=1 and use a mapped network drive. With the run options below, we run two scratch locations, a local folder on the C-drive and a network drive with a limitation of 2 GB mapped to the computers Z-drive. 

–tmpdir {C:\tmp} –tmpdir {filesize=2,slow=1,Z:\network_drive\tmp}

I/O TMPDIR

https://2021.help.altair.com/2021.2/hwsolvers/os/topics/solvers/os/tmpdir_io_r.htm?zoom_highlight=SCRFMODE [https://2021.help.altair.com/2021.2/hwsolvers/os/topics/solvers/os/tmpdir_io_r.htm?zoom_highlight=SCRFMODE]

Run Options -tmpdir

https://2021.help.altair.com/2021.2/hwsolvers/os/topics/solvers/os/run_options_os_r.htm [https://2021.help.altair.com/2021.2/hwsolvers/os/topics/solvers/os/run_options_os_r.htm]