Next step would be to double check the fuse listed for the reversing lights.
Then locate the reversing light switch on the side of the gearbox. Connect
the 2 wires going to the switch with a fuse wire. Turn on the ignition and the
reversing light should be on. There may be more than one switch on the
gearbox so be careful.
Let us know how you get on and then if that didn't work you can go for plan
B