How do I make a collision condition within the action?

I want to add a shield power up and it is a shooting game. So what I want to do is on click shield then I will set the shield variable to 1. Then in the next event define Shield=1 and I want to add an action that is bullet on collision with character subtract 3 from person health. How do I do this but only when shield is 1 when shield is 0 it subtracts 7.

Here is an image

Add sub-events below the condition bullet collision with the person:

If Shield = 0 => HP -7

If Shield = 1 => HP -3