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To show the Newsletter input field you need to install the Contact Form 7 plugin.
When you activate the plugin you will find a Contact option on the Dashboard.
Add a contact form and it will generate a Shortcode which you have to paste in the customizer.
Refer the Image: https://www.themeseye.com/demo/multipurpose-ecommerce/documentation/images/news1.png
If you need further clarification please hit a reply.
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