I want to enable/disable notifications from application.

Here are the instructions on how to set notification preferences:

To turn notifications on or off, go to the settings on your device > tap “Apps” > choose the Muscle Booster app > select “Notifications” > then turn notifications on/off. 

For further customization, tap the settings icon in the upper right corner of the “Plan” screen > open “Reminders” > then select which settings you'd like to turn on/off.