Hi,
Use this.
Var1=userresponse("3.End Date(mm/dd/yyyy)")
Header Var2=If([Var1]="Today") then currentdate() elseIf([Var1]="Yesterday") then RelativeDate(currentdate();-1) elseIf([Var1]="Yesterday-7") then RelativeDate(currentdate();-7)
elseIf([Var1]="Today+90") then RelativeDate(currentdate();90)
Amit