I am using Sony (Android 6.0)

Step 1: Go to Settings, either from the app drawer or from the notification panel.

Step 2: Tap "Battery" from the Settings list and then click on "Battery optimization" option from the top-right menu icon.

Step 3: Select "All apps" from the options to bring the list of all the apps on which doze mode is enabled.

Step 4: Choose Skooly app to disable doze mode.

Step 5: Tap "Don't optimize" and then click "Done".