Hello,
Thank you for contacting NXP support.
To enable the Relative Humidity Measurement cluster in the code to be built, it is
necessary to add the following to the zcl_options.h file:
#define CLD_RELATIVE_HUMIDITY_MEASUREMENT
I highly recommend to give a look into the ZigBee Cluster Library User Guide on the Chapter 28 you will find the Relative Humidity Measurement cluster that I think you will find useful for the implementation of this cluster.
Please let me know if you have any question regarding this.