To try to rephrase, are asking how to filter to show the last full calendar week (Sunday to Saturday)?
If that's the case, you could create an additional calculated field:
IF DATEPART('week',[DateField]) = DATEPART('week',[DateField])-1
Then, just add that new field to your filter.
Another approach you may find useful is to simply create 2 parameters to allow your users to select start date and end date range they choose.
1) Create a date parameter as Start Date
2) Create a date parameter as End Date
3) Create a calculated field as:
IF [DateField] >= [StartDate] AND [DateField] <= [EndDate]
You can drag that calculated field into the filter and then the user can set the date endpoints as desired.
Hope this helps!