The Arduino IDE provides an excellent library package manager where versions of libraries can be downloaded and installed. This Github project provides the repository for the ESP32 BLE support for Arduino.
The actual source of the project which is being maintained can be found here:
https://github.com/nkolban/esp32-snippets
Issues and questions should be raised here:
https://github.com/nkolban/esp32-snippets/issues
Documentation for using the library can be found here:
https://github.com/nkolban/esp32-snippets/tree/master/Documentation