Hi,
Auto retro account till which period or like 2 month back every time or which way they want auto retro accounting?
You may User RPUTRBK0 report to set retro accounting date for all employees in IT0003.
However, I would suggest to set force retro accounting date in Payroll driver screen if client want to for all employee. There is field called Force retro accounting.
and 3rd way is variant. While creating variant, there is option to automatically set date from system date or period Like.
If today's date is 27.12.2015 and client want 27.09.2015 (3 Months back) then while creating variant, you may use sy-datum - 3 Months. and schedule payroll.
Thanks,
Ketul