DA14531: Modify ble_app_peripheral example to read button state


I am new to wireless communication. Recently, I bought a DA14531 USB evaluation kit and programmed it with the ble_app_peripheral example ((SDK6.0). I can control the LED on the evaluation board from the LightBlue app on my phone. Next, I would like to read the state of the push button on the evaluation board and automatically update the value in the LightBlue app when the notification is enabled. I have reviewed the code for many hours but no success so far. Also, I searched for read/notify examples without success. If possible, can you please point to the examples or the code where I can enable this functionality? 

Thank you so much for your time.