`AgNO_3_(aq)+KI_((aq)) rarr AgI_((s))+KNO_3_(aq)`
This is already a balanced equation.
When we add KI to `AgNO_3` as the result AgI will precipitate. So the net reaction will be the reaction of `Ag^+` and `I^-` and the formation of AgI precipitate.
So the net ionic reaction will be;
`Ag^+_(aq) + I^(-)_(aq) rarr AgI_((s))`
It's balanced already.