Macro for Renaming the whole row except first cell

Option Explicit

Sub Macro1()
    Dim FillRange As String
    
    With Sheets("sheet1")
         FillRange = "B1:" & .Cells(1, Columns.Count).End(xlToLeft).Address(0, 0)
        .Range("B1").Select
        ActiveCell.FormulaR1C1 = "Act1"
        .Range("B1").Select
        Selection.AutoFill Destination:=Range(FillRange), Type:=xlFillDefault
        .Range(FillRange).Select
    End With
End Sub

How do you identify which one is the first...name???

Option Explicit

Sub Macro1()
    Dim FillRange   As String, _
        CurrentTab  As Worksheet
    
    For Each CurrentTab In ThisWorkbook.Sheets
        If CurrentTab.Name <> "the first one" Then
            With Sheets(CurrentTab.Name)
                 FillRange = "B1:" & .Cells(1, Columns.Count).End(xlToLeft).Address(0, 0)
                .Range("B1").Select
                ActiveCell.FormulaR1C1 = "Act1"
                .Range("B1").Select
                Selection.AutoFill Destination:=.Range(FillRange), Type:=xlFillDefault
                .Range(FillRange).Select
            End With
        End If
End Sub