With so little information, it's difficult to make a suggestion. But I'll try to point you in the right direction.
You can make non-payslip Salary Heads in Attend HRM. That makes it easy to define as many salary variables as you want.
So, first create a non-payslip salary head called 'Wages for a day'. Wages for a day = Wages for the month / Days in the month.
Now, make another non-payslip salary head called 'Payable Days'. Payable Days = Days in the month - Days absent (or something similar).
Now, Pay = Wages for a day * Payable Days.
Hope this helps, if it doesn't write to email@example.com
to schedule an online support session.