How to manage the app optimization on Galaxy s4?

I have Galaxy S4 model GT-I9505 running Android 5.0.1 and says that last updates are installed.
Few days ago I received the app optimization notification and I changed the settings for most apps. Unfortunately now whatsapp does not show any notifications. I understood that I should have not changed the setting in the app optimization.

Now, I'm not able to find the setting page for app optimization.
I have the 'Smart Manager Provider' app that includes Battery, Storage, RAM, and Device Security. However under battery I do not find the app optimization setting. i only get the usual green battery with the charge percentage (with a 'battery usage' button), abnormal battery usage (with 'details' button that is currently inactive), and Remaining battery power with a switch to show power on status bar.

I was waiting in hope that I will get this 'automatic' notification again, but it still did not appear. Any idea when or why this notification appears?
How can I change the setting of the app optimization now?

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