I really suggest writing more precise titles that can shortly describe what you need help with.
When I see something like "small help" I am not exactly excited to open up the thread.
Not trying to be impolite.
As for your problem, it's better to do what Footman16 said: disable the experience gain for a specific hero or heroes, not for every hero through the gameplay constant.
One thing I can suggest is for you to quickly look at every single trigger event and action and most of the conditions since most problems like this one can be easily solved on your own (in my opinion).
It will take you some time but you won't have to wait for someone else to solve such an easy problem, meaning that you can move on to bigger and more complicated tasks/problems and ask for help for these advanced tasks.