I want to copy a value from a previous sheet, every day.

[SamT]

Dim ShYName As String, ShTName As String

ShYName = Format(Date - 1, "dd-mm-yyyy")
ShtName = Format(Date,"dd-mm-yyyy")

Sheets(ShTName).Range("I34") = Sheets(ShYName).Range("I35")
End Sub

Or

Dim YValue
YValue = Sheets(Format(Date - 1, "dd-mm-yyyy")).Range("I35").Value
Sheets(Format(Date,"dd-mm-yyyy")).Range("I34") = YValue
End Sub

Lastly

Sheets(Format(Date,"dd-mm-yyyy")).Range("I34") = Sheets(Format(Date - 1, "dd-mm-yyyy")).Range("I35")
End Sub