How to change label text from another procedure in web C#

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Data;
using System.Configuration;
using System.Data.SqlClient;
using System.Threading;
using System.Text;
using System.IO;
using System.Net;
using Oracle.ManagedDataAccess.Client;
using System.Globalization;
using Ionic.Zip;

public partial class ACD_Test : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {

    }
    protected void Button1_Click(object sender, EventArgs e)
    {
        Zipdownloadfile(Main.ServerPath() + @"TempFile\Income_statement_AACS\Iqube", "sqmr");
    }

    public static string Zipdownloadfile(string pathdownload, string filenamezip)
    {
        var logerror = "";
        try
        {
            using (ZipFile zip = new ZipFile())
            {
                zip.AlternateEncodingUsage = ZipOption.AsNecessary;

                string[] ArrayFile = Directory.GetFiles(pathdownload);
                foreach (string NameFile in ArrayFile)
                {
                    zip.AddFile(NameFile, filenamezip);
                }

                System.Web.HttpContext.Current.Response.Clear();
                System.Web.HttpContext.Current.Response.BufferOutput = false;
                System.Web.HttpContext.Current.Response.ContentType = "application/zip";
                System.Web.HttpContext.Current.Response.AddHeader("content-disposition", "attachment; filename=" + filenamezip + ".zip");
                zip.Save(System.Web.HttpContext.Current.Response.OutputStream);

                foreach (string NameFile in ArrayFile)
                {
                    File.Delete(NameFile);
                }

                System.Web.HttpContext.Current.Response.Flush();
                System.Web.HttpContext.Current.Response.SuppressContent = true;
                System.Web.HttpContext.Current.ApplicationInstance.CompleteRequest();
            }
        }
        catch (Exception ex)
        {
            logerror = ex.Message.ToString();
        }

        return logerror;
    }

}