It IS available. If you haven't set it up, do it in Chart of Accounts. Otherwise, "Employees", Run payroll Checkup and as you hit next, next, & come to that page showing this set up in a list of other deduction types, click on whatever you named it, and it has the same adjustments & set up there.

A % of paycheck, an exact amount (PER month due), max if needed depending on the schedule, and a time schedule. We have one set to "1st of each month" it starts over at zero. 

Hope that helps