Two things I am assuming.  One, that the above formula is the select formula.  Second, that you would need a parameter or two.  So we only need to focus on the  date({incident.inc_resolve_act}) = LastFullMonth statement.  To get a specific month number you would probably use something like this; month(date({incident.inc_resolve_act})) = {?monthParameter}.  To get a range of months (not considering years) you could do something like this; month(date({incident.inc_resolve_act})) >= {?begmonthParameter} and ; month(date({incident.inc_resolve_act})) <= {?endmonthParameter}

So do you want from January 2015 to present or just January 2015? 

Now that begs the question, how is the user going to input the parameters.  Actual date, Month name and year, some other string format (YYYY/MM), etc.