Want to change self cast key bindings

I have 'attack-move' on tab. If I'm playing a champion like Nami, and self casting my e during attacks, I often accidentally Alt+tab my client. This is because her e can be applied whilst the projectile is in the air. I will be pressing Tab to attack while pressed alt+e to self apply my e, and this will cause the window to swap.

I would like to change self cast to c+q/w/e/r but it won't allow this combination. How can i change this?