Connecting newsletter subscription form to 3rd party service

[PavelLin]

Hi everyone, I've connected my Shopify email subscription form to a 3rd party service. On subscription, the customer's email is sent to the service and added to my company's database. To do this, I've amended the newsletter.liquid, and it works fine, except: the customer's email is still also captured by Shopify, which I'd like to avoid.
I found it's caused by this part of code: 

I need to amend and delete it, but I cannot find the <form> parameters in any file. Any ideas where it can be found and amended? In the newsletter.liquid, it's just:

{%- when 'email_form' -%}
<div {{ block.shopify_attributes }}>
{% form 'customer', class: 'newsletter-form' %}
<input type="hidden" name="contact[tags]" value="newsletter">
<div class="newsletter-form__field-wrapper">
<div class="field">
<input
id="NewsletterForm--{{ section.id }}"
type="email"

Any ideas appreciated, thanks!