ReSpeaker 6-Mic microphone data type and FFT

Hey, I’am working on project that require FFT from microphone data. I’am using the ReSpeaker 6-Mic Circular Array kit and pyaudio to capture mic signal. I want to have the data showed in SPL dB. Soon I will be doing a calibration of these mics but i’am having issues with understanding how the data is converted from MEMS mic availabe on the board. Is it transfered through AC108 via PCM line? Maybe someone did similar thing and could tell me what is the best way to convert this data to decibels to have more accurate results?