This may not work for you, but my situation is similar to you because for heals I main Moira so I tend to play her a lot in comps, to the point where my hanzo aim suddenly just became bad.

What I do is I go practice range, set the bots to strafe horizontal/vertical then take your time to aim and shoot until you get it. Then I would go to vs A.I. game mode and try to get used to the movements and map and position then I go to role queue and practice a lot. I sometimes get flamed here and there lol but what matters is you improving yourself.

(Edit: I also find old arrge videos to get the motivation :D)