Change the existing neon Customizer on a template using a legacy theme

1. In your Shopify admin click  Themes, click Actions and Edit Code next to the theme on which your existing customizer is currently installed, I am using the Debut theme for the demonstration:

2. Find the existing template on where your customizer is currently installed on. If you don't remember the template name you can find it by doing the following. 

1. In the Shopify admin, go to Products or if the customizer is on a page Online store -> Pages
2. Scroll down until you see the Theme Template section, 
3. In the example image below our template name would be product.neon-product-customizer.liquid

3. Open the file in the code editor and find code that looks like this

<div id="neon-customiser-app"></div>

4. Find the neon customizer ID you would like to replace the existing neon customizer with.

1.  In Shopify admin go to apps -> Neon Product Customizer
2. Click on Customizers in the top right corner
3. Make note of the customizer ID in the list 

5. In the Shopify Theme code editor modify the existing HTML that renders your neon customizer and add this HTML attribute  data-customiserid="304", it should look something like below just replace the number with your ID.

<div id="neon-customiser-app" data-customiserid="304"></div>

6. In the code editor hit save.

You are all done! 

Note: If the above template was created as a page, you can follow the same instructions. Refer to the Pages section from your Shopify admin, create a new page, change the theme template under Online Store to the newly created template and click Save. You can also refer to the Navigation and can link it with the page or product.