@sportarainbow if you want to do this directly in your theme code, here's the approach I take:
1) Decide where you want the link. For example let's say you want to change the add to cart button to "buy here" and link to them.
2) Duplicate your live and work off the backup theme so that your live site is not affected.
3) Find the code that controls that element. This article will help you identify elements from within your browser, or you can read the code in your theme files - Start with the Template product.liquid, then look for included Sections or Snippets, then read those files, eventually you'll find the add to cart button.
4) Now replace the add to cart button with your link, something like this:
{% if product.vendor == "Some Supplier" %}
<a href="https://thelink" target="_blank" class="add-to-cart">Buy it here</a>
{% else %}
<!-- leave the regular add to cart button code here -->
{% endif %}
- target="_blank" is optional, this will open the link in a new page. Some people say not to use these, some people say use them when it makes sense. In your case, it's sending the customer to a different site so you may want to keep it, assuming they will still want to have your site open while looking at buying that product.
- class="add-to-cart" controls the styling, that class name is just an example, assuming you'll want to style the button the same as your add to cart button you'll want to copy the same styles / class as the button (which that article I shared can help). Of course you can style it however you want by adding CSS to it (see that article for adding custom CSS).
+1 on @Kimi 's answer for the easy solution. I offered this solution because if you can code a feature directly into your theme code, that's the fastest method performance-wise - adding 3rd party apps that interact with your storefront often slows down the page load time because of extra resources being loaded so by habit I prefer to edit the theme directly.
Good luck, remember to do any work on a backup theme in case you make a mistake. If you need help from a developer feel free to reach out to my team at speedboostr.com/contact.
