relink.cs

InDesignServer.Objects allGraphics = this.document.AllGraphics;//your indd document

                this.basePath = "C:/myimages/";
                
                foreach (dynamic graphic in allGraphics)
                {
                    InDesignServer.Link link = graphic.ItemLink;
                    
                    string path = link.FilePath;
                    
                    string fileName = this.basePath + "/" + link.Name;

                    object fileSystemObject = Microsoft.VisualBasic.Interaction.CreateObject("Scripting.FileSystemObject", "");

                    Type fileSystemObjectType = Type.GetTypeFromProgID("Scripting.FileSystemObject");

                    object file = fileSystemObjectType.InvokeMember("GetFile", System.Reflection.BindingFlags.InvokeMethod, null, fileSystemObject, new object[] { path });
                    
                    link.Relink(file);

                    link.Update();
                }