Changing arrow damage

[BluePenguin_Won]

I want to make my bow to shoot arrow at custom damage.
here's my code:

on rightclick holding bow:
    if name of player's tool contains "&bStrong bow":
        cancel event
            make player shoot an arrow at damage 15

But skript says there is no condition/effect
pls help

 

[Bell O'dell]

use reduce or increase damage and a damage event instead