in Save button click init value can be change

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ASP.NET

Protected Sub Page_Init(sender As Object, e As System.EventArgs) Handles Me.Init
    startDatelbl.Text = New DateTime(Now.Year, Now.Month, Now.Day)
End Sub

in above code store the label current date.
But i can add two button next And Prev in my code
when next button click 21 days add in startdatelbl.
but when click save button, page is load and startdatelblvalue can chage and list view fill from starting. startlbldate change value