Is there another idiom for using too strong a tool for the job: not "bring a gun to a knife fight" or "use a sledgehammer to crack a nut"? Or turn it around - one about using a simpler, more direct tool? It may be "kill a fly with..." But nothing I end it with sounds like what I a, looking for. Bazooka, maybe.
Googling "using a * to kill flies" (with a wildcard) yields, in the first two pages of results,
as well as flyswatter. So it's clear that using X to kill flies is an established idiom, but there's no single word that is predominantly used for X. Pick your favorite weapon or tool and insert it.