There is not a way to recalibrate the internal CPU clock, this calibration is trimmed by factory. Nonetheless, could you please give us more information related with your application or reason behind the need to calibrate the internal CPU RC clock? Could we help you with something else?
Best regards, Raul.
I want the internal RC/External Oscillator to be very Accurate.
in some CPUs we can calibrate the internal RC with External LOW OSC 32768 for example.