To start adding products for each answer click Link Products. You can filter the products in your store by their title, using the search bar or by their tags. To filter using tags enter the following in the search bar tag:xyz where 'xyz' is the actual tag applied to your products.
The process for linking variants is exactly the same, simply click the Link Variants button instead.
If you want to keep the products in your quiz updated based on their tags, we recommend linking them via automated collections. You can easily create automated collection inside Shopify based on product tags and once linked to your quiz, you can keep automated collections up to date with new inventory or existing tag changes using the resync function. For more details please check out the following article.