You can access the setting by taping Menu on the main command interface and More > Settings after that.
The settings menu allows you to manage sounds, game language and features such as:
Starting a new game: Note that this will reset all your current progress!
Linking in-game progress with a gaming service account.
If you wish to reduce the notification you can select any of the option to turn on or off. We are constantly trying to improve this section so the information will be valuable and informative for you, Commander
Warfare - when your city, resource tile or reinforced ally is attacked, scouted or combat has begun and when enemies retreat
Alliance - when alliance buildings are attacked or scouted; when new commands are issued and when technology contributions are available
Development - when construction, recruitment, recovery, crafting, part production or improvements are completed; whenever science points and general energy are fully recovered as well as as add-on ability cool-downs expire
Event - when events are about to start (Kill, Gather or Power events, Updates etc.)
Messages - when receiving a new message from alliance members or non-allied commanders
Benefit Passes - when Benefit Pass rewards are ready for collection
Protection - when protection boosters such as Peace Shield or Anti Scout are about to expire
Note: The Warfare and Alliance Spam Protection features allow to turn off notifications from attacks with less force than a value of your choice (up to 50K). Additionally attacks with lower force than the specified Spam Protection value will not trigger the in-game Alert Overlay.