nrf52840 ncp bit rate

Hello everyone!

I have started to work with openthread recently, and now I have to build a mqttsn client into a stm32 uController.

I'm doing that by using the spinel protocol between stm and a nrf52840. The nrf52840 is configured as NCP.

The problem actually seems to be very simple: I just want to change the transmition speed to increase the module's range, but I couldn't find where i should change it inside the NCP's example file in the nRF5_SDK_for_Thread_and_Zigbee_2.0.0  (I'm programming the board using segger IDE, inside Windows 10 OS)

So I was hoping that someone here should know something :D

Thanks for any help!