Updated:
You can try adding this line to show the button:
<input type=“submit” value=“Send mail”>
Like below:
<!-- Begin MailChimp Signup Form -->
<!-- put your url from MailChimp form into action=“your link here” -->
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<form action=“#!” method=“post” name=“mc-embedded-subscribe-form” class=“gk-newsletter” target=“_blank” novalidate=“”>
<label for=“mce-EMAIL” class=“element-invisible”>Email</label>
<input type=“email” value=“” name=“EMAIL” class=“required email” id=“mce-EMAIL” placeholder=“email”>
<input type=“submit” value=“Send mail”>
<!-- real people should not fill this in and expect good things - do not remove this or risk form bot signups-->
<div style=“position: absolute; left: -5000px;” aria-hidden=“true”>
<label for=“mce-absolute” class=“element-invisible”>Name</label>
<input id=“mce-absolute” type=“text” name=“b_6601f0307e28eefdfd842bbdd_2007e79bce” tabindex=“-1” value=“”>
</div>
</form>
<!--End mc_embed_signup-->