Write into database a field added to Shopware 6 form via template

Can someone give a tip on where to look further to write for later use in database such a field added to Shopware 6 form via form template:

{% block cms_form_newsletter_input_company_name %}
{% sw_include ‚@Storefront/storefront/element/cms-element-form/form-components/cms-element-form-input.html.twig‘
with {
fieldName: ‚companyName‘,
additionalClass: ‚col-md-4‘,
label: ‚newsletter.labelCompanyName‘,
placeholder: ‚newsletter.placeholderCompanyName‘
}
%}
{% endblock %}