You didn't mention what version of the software you're using. I'll assume you're on the latest. If that's the case, there is a File -> Import -> MCM item in SiP Layout that can be used to import and MCM database and convert it to a SIP drawing. This will update all dies to place them into die stacks, among other things.
Yeah. The version of the software is important. I might be the cause why you have experience such problem.
I am using 16.5 version, I have a .sip file and want to convert to .mcm. I don't see anything in import/export as you mentioned
above. I also want to later convert .mcm back to .sip. Please help
16.5 SiP Layout XL includes menu items for importing and exporting MCM databases from SIP. They are located at:
File -> Export -> MCM and File -> Import -> MCM
If you don't see these, then you may have an old menu file, you may have modified your menu files unintentionally, etc. The commands are "mcm export" and "mcm import", respectively, from the command line. Hope that helps. If you're using a non-layout SIP tool, such as the SI product or the architect tool, I do not know that these include this capability. Note that there is data loss in the conversion, of course, since you are moving to a lower-tiered tool with less functionality (such as lack of die stacks, spacers, interposers, etc).