how to change Post Process material parameters in game?

hello everyone. i’m working on a game where at some point you wil obtain x-ray vision. so i made a post process material and that works (see image 1) i also made a parameter: alpha
with this parameter i can make the post process material invisible (see image 2) the only problem is that i have no idea how to change this parameter in game :frowning: (see image 3).
if anyone knows how to do this please reply

thanks in advance :slight_smile: