Dim I As Integer
    Dim SheetExsits As Boolean
    
    'initalise SheetExsits
    SheetExsits = False
    
    'Check if SheetName Exsits
    For I = 1 To Worksheets.Count
        If Worksheets(I).Name = "Sheet3" Then
            SheetExsits = True
            Exit For
        End If
    Next I
    
    'display messagebox with position
    MsgBox I

' add this code

Function SheetExists(sheetname) As Boolean
'   Returns TRUE if sheet exists in the active workbook
    Dim x As Object
    On Error Resume Next
    Set x = ActiveWorkbook.Sheets(sheetname)
    If Err = 0 Then SheetExists = True _
        Else: SheetExists = False
End Function

' Call it from your procedure in the same or another module.
' like this
' This will work using the sheet name or an index number of the sheet

Sub myproc()

    If SheetExists("Sheet1") Then
        Sheets("Sheet1").Activate
    Else
        Exit Sub
    End If

End Sub