The command re-roll would need to happen right after the three dice were rolled.
BRB rulebook update 1.3 :
Q: Can I use the Command Re-roll Stratagem to retroactively
re-roll a dice? For example, if I take a Psychic test, and
then my opponent successfully Denies the Witch, could I use
the Stratagem to try and increase the result of the original
Psychic test?
A: No. You must use the Stratagem as soon as you have
rolled your dice, before anything else occurs.