There's no utility or method to decompile a DMCL load module and get the source syntax.
However, there are two ways to get information about what is in a DMCL load module which can be used to create compatible source.
Punch the DMCL load module in hex, and use the DSECTs to interpret what's there
Issue a LOOK DMCL or run IDMSLOOK in batch against the DMCL. The LOOK utility will read the load module and produce a report of what it contains. Then create DMCL source based on that information. Use the following syntax in batch:
DMCL ALL SORTED
The easiest approach is to recreate source based on the information from the LOOK output (option #2 above).