How to build an app to send user defined character through Bluetooth to Arduino

I'm not a programmer and i just want to make and app for my Arduino project. Can anyone here help me to build an app to send character to my Arduino through Bluetooth ? The sending character can be define by the user at the beginning. i found the exact same app that i want but i cant use that for my project.

Which version of BlueTooth are you using on each end?

Which devices on each end?

I created a playlist on my channel about Arduino AppInventor 2 via Bluetooth, from the connection to sending and receiving digital and analog data (including texts) and with a small HMI. Maybe this can help.