DSXchange

I am passing parameters to a Job activity in the sequence. I have two parameters current month (YYYYMM format) and previous month (YYYYMM) format. Is there a way to derive previous month from the current month (preferably in the Value Expression section of the Job Activity)?

Please suggest.

...and you have the current month, right? Then it will be a matter of date arithmetic. Resolved the first day of the current month and substract 1 day to it.
OConv(Iconv(CurrMonth:"01" ,"D YMD[4,2,2]") - 1), "D YM[4,2]")

I would suggest to do this in a user variable and then pass the user variable to the job's parameter instead of doing this logic directly on the value expression for the paraneter

Take a look at the date Transforms supplied in every project. There are useful, pre-defined Transforms for things like MONTH.FIRST and MONTH.LAST, which can recognize a MONTH.TAG structure such as you are using.