You might do best playing around with a query based on the DateAdd function. Read up on this in the Help files including the examples.
If you run your report for the previous month on the first day of this month, you would base that report on a query selecting on your date field using a criterion that looks something like
>=DateAdd("m", -1, Date())
On the first day of a month, the above should return a date equal to the first day of the previous month. And that IS the 'greater than or equal' operator in front of that clause.
If you didn't want to include today (because it is the first of this month), then select the date TWICE in your query and make the second date's criterion (on the same line as the first criterion)
<Date()
That IS the 'less than' operator in front of the Date function.
The SQL for this query (if you look at it that way, and assuming the field name is [Job Date]) should then include something like
... WHERE [Job Date] >= DateAdd("m",-1,Date()) AND [Job Date] < Date() ...
Before anyone asks, this is easier than using BETWEEN ... AND ... because I am assuming Mark B does NOT want to include today's date in last month's report. This is, I think, the EASIEST method to do that. Using BETWEEN would require a second DateAdd function.