In this text file I will explain exactly what i have done.

1) On the nRF52840-DK with nRF programmer I write this hex file :
directory : nRF5SDK160098a08e2\examples\ble_peripheral\ble_app_hrs\hex
file : ble_app_hrs_pca10056_s140

2) I program the dongle nRF52840 with nRF connect Bluetooth Low Energy.
   Like this the dongle become nRF52 Connectivity

3) I download the pc-ble-driver-py library with this command :
   pip install pc-ble-driver-py

4) I download the heart rate collector example in the python file test_heart_rate_collector.py

5) I run the script in the cmd windows : python ./test_heart_rate_collector.py