The combo and Listbox in Access are different from VB. They do not have Add or Insert methods
You can insert an activex object Microsoft Forms Combo which is the same as VB component.
In Access there is a property Row Source type. This should be set to Value List.
You have to define the Rowsource property of the ListBox
The following code should work
For i = 0 to 6
MyCombo.rowsource = MyCombo.rowsource & DateAdd("d",-1*i,date) & ";"
Next
PS: The column count property should be 1. If you have more than 1 then that many strings separated by ; should be added to rowsource
Best of luck