How to show/send text to BLE LED matrix device form Android App?

I am working on one POC to show text from an Android app in an LED matrix device (BLE device). Till now I have done below steps -

1. I can connect with the BLE device.
2. I can connect with the GATT server.
3. I got characteristics of the BLE device which are READ, WRITE WITHOUT RESPONSE and NOTIFY.

Now how I can send and show a text to the LED matrix device?

While searching I found some folks who have done this POC using MIT App Inventor with Bluetooth Arduino and I don't have any idea about these. So can I achieve this using Android SDK or any android Library?

Please guide me, Thanks in advance.