Thanks
Thanks to the authors of those pages / pieces of code :
https://github.com/gdsports/midi-wifi-demos
https://github.com/neilbags/arduino-esp32-BLE-MIDI/blob/master/BLE_MIDI.ino (write midi messages)
https://gist.github.com/johnty/cbfa66c3369a692410f3493c20b2b3e2 (read and write)
https://circuitdigest.com/microcontroller-projects/esp32-ble-client-connecting-to-fitness-band-to-trigger-light (initiate the connection to another bluetooth device)
and the Arduino BLE_Client example sketch for ESP32 boards
This project is to modify circuit bendig and is based on the code of the previous projects.