Default the Mailchimp selection to subscribe

default-mailchimp-to-yes.php

<?php
function my_mailchimp_tribute_by_default() { ?>
	<script>
        jQuery("input[name=give_mailchimp_signup]").prop("checked", true);

	</script>

<?php }

add_action( 'give_donation_form_after_submit', 'my_mailchimp_tribute_by_default' );