Hello,
If you want just to add some content below the short product description you can use woocommerce hooks to make changes. Here you can find WC hooks for the single product https://businessbloomer.com/woocommerce-visual-hook-guide-single-product-page/ Also, watch video tutorial to understand how it works https://www.youtube.com/watch?v=JHN7viKRxbQ
Use child theme to make changes.
Regards
