How to make Zap gun headshots in Respawnables game ?

Hi guys, this question is about mobile game I play and I hope like me many people here plays games on mobile. So this game I play named as "The Respawnables" is very nice third person shooter game for android and I enjoyed it so far. But now in mission mode, I am supposed to take headshots using zap gun. I have purchased this but its quite difficult to take shot from this gun. Is there any technique to make headshot using this gun or atleast get aiming right ?

Looks like there is no auto aiming or this zap gun gets fixed on targets by its own.. mostly around target but not on target. The gun is unlocked at level 50 and from mission provided for this gun I feel it is quite powerful and I don't know way to use it. One of the mission is to take down 25 enemies in single match using zap gun.. is it even possible ?

Well, I have played that game but not yet reached level 50 to get the Zap gun, nor have that much game cash to buy it yet. But seeing this video review, I think zap gun doesn't come with auto aim and you have to be expert enough to use it. May be they assume that by level 50 you are pro in game and should be able to handle it.

https://www.youtube.com/watch?v=Qztmlec6fyg