answer to my question,

1. create a static class
2. create a static method as below
3. overwrite the value of the property

4. call event from your xml config file in the editor tag.

   using Eksponent.Dewd;
   using umbraco.BusinessLogic;
   
   
   public static class MyClassEvents
   {
       public static void BeforeSave(object sender, BeforeSaveEventArgs e)
       {
           // tab name _ property name 
           e.Values["Properties_Last Modified By"] = User.GetCurrent().LoginName;
       }
   }
   

this is event tag within the editor tag

event handler="NameSpace.MyClassEvents.BeforeSave,AssemblyDll" name="BeforeSave"