In your first post you refer to a report, but in the last post to a form. The method of sorting differs in each. With a form you can either order the form's underlying query with:
ORDER BY Abs([Service_Completed])
or you can set the form's OrderBy property to:
Abs([Service_Completed])
and in the form's Open event procedure put:
Me.OrderbyOn = True
In a report you should use the report's internal Sorting and Grouping mechanism and create a group level on the expression Abs([Service_Completed]).
This works because Access implements a Boolean TRUE as -1 and a FALSE as 0, so returning the absolute value with the Abs function allows the FALSE values to sort first as 0 sorts before 1. If you regard this, as the head of one software company of my acquaintance
calls it, as 'being unduly chummy with the implementation' you can use one of the following expressions:
IIf([Service_Completed],1,0)
or:
Not [Service_Completed]
or:
([Selected]=False)
instead of calling the Abs function.