See below:
<!-- Begin MailChimp Signup Form -->
<div id="mc_embed_signup">
<form action="https://xxxxxxxx.us1.list-manage.com/subscribe/post?u=xxxxx&id=xxxxx" method="post" id="mc-embedded-subscribe-form" name="mc-embedded-subscribe-form" class="validate" target="_blank" novalidate>
<label for="mce-EMAIL">Subscribe to our mailing list</label>
<input type="email" value="" name="EMAIL" class="email" id="mce-EMAIL" placeholder="email address" required>
<div class="clear"><input type="submit" value="Subscribe" name="subscribe" id="mc-embedded-subscribe" class="button"></div>
</form>
</div>
<!--End mc_embed_signup-->
Your need to use the areas that are bold in the below.
https://xxxxxxxx.us1.list-manage.com/subscribe/post?u=xxxxx&id=xxxxx
The Action will be different for you don’t add the https://
An example:
xxxxxxxx.us1.list-manage.com