Is there any way to add just an icon to a MailChimp embed form 'submit' button?

I'm using a MailChimp embed form to collect email addresses for a newsletter.

My client's design uses just a right arrow instead of the word "Subscribe", however, when I try to put any other value aside from text in the "value" section, it outputs raw data vs font-awesome.

Is there a way to manipulate the submit button's "value="Subscribe" in the embedded text to use an arrow like the screenshot attached (Client design)?

<!-- EMAIL INPUT -->
<div id="mc_embed_signup_scroll">
    <input type="email" value="" name="EMAIL" class="required email" id="mce-EMAIL">
    <input type="submit" value="Subscribe" name="subscribe" id="mc-embedded-subscribe" class="button">
</div>

Client's design:

The result if I try to use Font Awesome as a value:

I've also tried to use CSS and content"" but that didn't have any effect.

.tertiary_btn.et_pb_button:after {
  font-family: "Font Awesome 5 Free"!important;
  font-weight: 900;
  content: "\f178";
  padding-bottom: 5px;
  display: block;
  font-size: 25px;
  opacity: 1!important;
  transition: none!important;
  margin-left: 8px;
  position: relative;
  margin-top: 4px;
  color: inherit;
}

I also looked into their "fredicons" but I am not sure if these are meant to be used with the embed forms as they too had no effect.

If you have had to use an arrow vs text within a MailChimp embed form in the past and know the best way to tackle this, please let me know. Thank you!