Using the console:
tgm
coc redrocketext
Go to the red workbench in the garage to enter workshop mode:
1. Build a small generator. (Power>Generators)
2. Build a quitting time siren. (Cage>Miscellaneous) and connect it to the generator
3. Build Red and Blue arena pads some distance apart (Cage>Arena) so they don't kill each other too quickly
4. Use the console to spawn some settlers (player.placeatme 20593 5)
5. Assign them all to the red rocket (press r while hovering over them in workshop mode then pick red rocket on the left side)
6. Command a settler to move to the red pad (Enter while hovering over settler to select them, then enter over the pad to tell them to go there)
7. Command a settler to move to the blue pad (see above)
8. Quickly exit workbench mode and activate the quitting time siren, this must be done before the fight ends.
If the fight ends too quickly you can always spawn a couple more settlers and try again.