Standard report Variant creation

Hi ,

i am trying to create the dynamic variant for standard report   RKWTP_CPTD, which contains the period and fiscal year fields on

selection screen, now i need to create variant as period has to  be current month -1 month i.e it has to show previous month

and for year , the current  year has to result in dynamic variant.

if any idea creating the variant please help me.

Thanks

SrInI