Hi.
You can use the action "Set Material Property Block Float" (
Ecosystem)
to change the value only on a certain object.
or
"Set Material Float" which will change for all objects that uses that material.
Material index in most cases is 0, unless you have a object with multiple materials.
The Named Float/Property Name depends on the shader.
if you select a material in the project window, then in the inspector on the title right click and select edit shader.
It will open the shader file and you can look there what name you need.
usually it has a underscore like this : _Opacity