I'm trying to connect two raspberry pi 3 betweem them via bluetooth.

But the fact is that their MAC addresses are AA:AA:AA:AA:AA:AA

Does anyone knows how to assign them a real mac address in order to be able to transfer data via bluetooth betweem them?

This is what hciconfig tells:

pi@raspberrypi:~ $ hciconfig
hci0:   Type: BR/EDR  Bus: UART
    BD Address: AA:AA:AA:AA:AA:AA  ACL MTU: 1021:8  SCO MTU: 64:1
    UP RUNNING PSCAN ISCAN 
    RX bytes:801 acl:0 sco:0 events:53 errors:0
    TX bytes:2526 acl:0 sco:0 commands:53 errors:0