PH 131 said:You can’t place a Warlock’s Curse on a creature that is already affected by your or another character’s Warlock’s Curse.
Hyena 2 has already been cursed by Jarl, who's first in the initiative order. I don't think it'd be unreasonable to rule that you can curse the next closest, cursable (is that even a word?) enemy to you, if you want to choose another target. Otherwise you can keep the same target, just without the curse.
It's also worth noting, at least as far as I can tell, that to get extra curse damage requires only that you attack a cursed target, not that it be a target that you cursed (which is different than say a pact blade that specifies a target you cursed).
Without the advantage of IG's ruling, you would still have the option by RAW of saving your minor action til after you attacked, if you killed the target you could curse whichever was the next nearest.
I think it is the spirit of the rules that that any benefits a warlock gets from a cursed enemy must come from his own curse and not that of another warlock.