The part number for reordering the RJ45 to DB9 adapter cable provided with PLC serial modules is Cable 14.
Pinout for the DB9 side:
This is a straight thru adapter cable, pin 1-1, 2-2, 3-3, etc. Pin 9 on the DB9 side is not used.
For the RJ45 side, while facing the module, the pins are numbered from 1 at the top to 8 at the bottom.