How to download all file from project folder in which starting name are same

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C#

ASP.NET

i need to download multiple file from project folder on button click. my files are place in the folder with following format:-

file_1_12_08_2020.txt
file_1_13_08_2020.txt
file_1_13_08_2020.txt
file_2_12_08_2020.txt
file_2_12_08_2020.txt

in this format i added date also in file name. now if i pass filename value as "file_1" then i want to download all file those name staring with "file_1".

What I have tried:

using (ZipFile zip = new ZipFile())
    {

                string fileName = "file_1_13_08_2020.txt";
                string filePath = Server.MapPath("~/User/JSON_Audit/" + fileName);
                zip.AddFile(filePath, "JSON Files");

        Response.Clear();
        Response.AddHeader("Content-Disposition", "attachment; filename=DownloadedFile.zip");
        Response.ContentType = "application/zip";
        zip.Save(Response.OutputStream);
        Response.End();
    }

i am trying this code to download file. but i enter full name then i able to download file. can any one suggest me the solution.