Beginner trying to read data from Arduino on to app

Hi, I'm working on a app that reads data from an Arduino via Bluetooth. I'm very new to this world. I'm using an RTC and a thermocouple connected to the Arduino that should be displayed on the app. I also need to be able to write back to the Arduino so that I may change the date and time on the RTC if it were to lose power and reset.

Where is the best place to start with this? Also i understand this isn't an Arduino forum but any knowledge about the code on that end would be helpful as well.