Simple theme

1. In your Shopify Admin click Online Store.
2. Click to Current Theme's Actions > Edit code.
3. Open the product-template.liquid file under the Sections area of your Theme Editor.
4. Copy the code below.

   <div class="product-single__cart-submit-wrapper{% if section.settings.enable_payment_button %} product-single__shopify-payment-btn{% endif %}{% if section.settings.add_to_cart_width == 'full_width' %} product-form--full{% endif %}">
   {% unless product.metafields.coattend.enabled %}
     <button type="submit" name="add" id="AddToCart" class="btn product-single__cart-submit{% if section.settings.add_to_cart_width == 'full_width' %} btn--full{% endif %}{% if section.settings.enable_payment_button %} shopify-payment-btn btn--secondary{% endif %}" data-cart-url="{{ routes.cart_url }}">
         <span id="AddToCartText">{{ 'products.product.add_to_cart' | t }}</span>
     </button>
     {% if section.settings.enable_payment_button %}
         {{ form | payment_button }}
     {% endif %}
   {% else %}
     <div class="coattend-button btn product-single__cart-submit{% if section.settings.add_to_cart_width == 'full_width' %} btn--full{% endif %}{% if section.settings.enable_payment_button %} shopify-payment-btn btn--secondary{% endif %}" data-cart-url="{{ routes.cart_url }}" data-coattend-product-id="{{product.id}}" data-coattend-variant-id="{{product.selected_variant.id}}">
        <span id="AddToCartText">{{ 'products.product.add_to_cart' | t }}</span>
     </div>
   {% endunless %}
   </div>
   </div>

5. Replace code from line 146 to 153. You can see what needs to be replaced on the below image. Simple theme code that needs to be replaced.
6. Click Save

Congratulations! Continue and display your event.