How to change newsletter preferences?

I had a look on Threadloom's site and I don't see anything about this, but..

I'd like to change to receiving text only emails. The newsletters look this this to me:
Code:
<!DOCTYPE html>
<html>
<head>
   <title></title>
   <meta name="viewport" content="initial-scale=1.0, width=device-width">
   <meta charset="UTF-8">

   <style>
       /* ------------------------------------------- */
       /* Elements */

       body {
           margin: 0;
           padding: 0;
           border: 0;
           background: #FFFFFF;
       }

       body,
       table {
           
               color: rgb(30, 54, 105);
           
           font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif, "Apple Color Emoji", "Segoe UI Emoji", "Segoe UI Symbol";
           font-size: 15px;
           line-height: 1.4;
       }

       a {
           
               color: rgb(42, 72, 136);
           
           text-decoration: none;
       }

       #address {
           
               color: rgb(30, 54, 105);
           
           text-decoration: none;
       }

       h2 {
           margin: 0 0 0.75em;
           padding: 0;
           font-size: 24px;
           line-height: 1.3;
       }

       img {
           border: 0;
       }

       p {
           margin: 0 0 20px;
           padding: 0;
       }

       table,
       tr,
       th,
       td {
           padding: 0;
           border: 0;
           vertical-align: top;
       }

       table {
           width: 100%;
           border-collapse: collapse;
       }
...
etc.

No, I will not change my email client to read HTML email. I also don't wish to unsubscribe from the newletter although I may if they are not going to be readable.

How can I make the change, or can an admin do this for me, please?

Thanks, Matt.