A voltage divider is usually completely unsuitable for powering sensors or modules as they draw too much (and variable) current.
If you are powering your Arduino from 12 volts, and using this same power supply to run your stepper motor you should be ok.
The Arduino has two on board power regulators, one for the Arduino MCU running at 5V and another that provides 3.3V for peripheral use. If your BLE module works at 5V then simply hook it to the Arduino VCC.
There is plenty of documentation on the Arduino variants, I've pointed to only one here.
Before you go further you should at the very minimum try to understand the configuration of the Arduino you are using. If you can understand the schematic, that is helpful too.