Hi Hyeongseok,
DDM function is only available in CMAQ-5.2_DDM-3D so far not in CMAQ v5.2.1, I think. Please see CMAQ-DDM for v5.3.3 - #2 by foley.kristen
In addition which version of MCIP do you use?
You need to use MCIP4.x instead of MCIP5.x to process WRF outputs when you generate meteorological data for CMAQ-DDM v5.2 (not v5.2.1) input.
Hope it is helpful.