As explained in the installation documentation
(plugins/reduce/doc/reduce.en.tm), you should copy the file
plugins/reduce/install/reducerc to your ~/.reducerc (this is on Linux; I
have no idea where reduce tries to find its initialization file on
Windows). It definitely should work with the psl reduce, provided that
rfpsl is in your $PATH. It used not to work with csl reduce. But I haven't
checked this for a long time; maybe, recent changes in csl reduce made it
compatimbe with tmprint.red.