In the Format event for the Report header you would put
Me.lblName.Caption = Date()- Weekday(Date()) + 8
This assumes two things. One is you don't have a field named Date in your Report because if you do Access is likely to make Date() into a field (at least that's what it did in my text report)so if you do you may need to use Now() and Format() out the time portion. Two, this assumes Sunday is the first day of week. If you have any other setting there you will have to test for that. But assuming you don't have either situation, the expression should work as posted. Change lblName to your label name.
Paul