Terminology is critical in IT, where similar terms may mean very different things. On an IBM mainframe, there is no such program as "iebgeneral" since program names for utilities are limited to 8 characters to comply with old operating system limits. There is an IEBGENER program, however.
"Concatenate" is a very specific term on an IBM mainframe, referring to the situation of having one DD name pointing to multiple data sets. You would "de-concatenate" this by using a unique DD name for each data set. If this is not what you want, you'll need to do a better job of explaining just what you are trying to do before we could help you. If you are wanting to split records in a single file into multiple files, this can be done by IEBGENER, IDCAMS, application programs, SORT, and possibly other tools depending upon what is available at your site.