That depends on what you mean by "expand a packed decimal". Do you mean to make a PD field larger, e.g. expand a 3-byte PD field to a 4-byte PD field? Or do you mean how to display a PD value in readable format? Or do you mean something else?
You need to be more specific about what you're trying to do. Show an example of your input records (relevant fields only) and what you expect for output. Explain what you're trying to do in terms of the example. Give the starting position, length and format of each relevant field. Give the RECFM and LRECL of the input file.