Load controller of a plugin in an other controller file

Hi there,
Wish good beginng of a week,
So i made a plugin opencart for 3.0.3.2
i want when i add to customer reward point with that + icon i call a function called process the process function is in my plugin controller which the name is ControllerExtensionModuleMembership ,
so i have looked for addReward() function and i found it in admin/controller/sale/order.php add this code
the problem that i get Uncaught Error: Call to a member function process() on null in
what should do where is the problem please thank you!

I would call the function like this:

You can do it like this:
But you also need to modify the process function to accept an array as a parameter.