If you only have one variant for the product then it’ll show the price & compare-at-price in the pricing box located under the main box ( title , media , category )

I found a solution ‼️ Go to Shopify admin , click products , click on the product you wish to change , once on the product page click the variant you wish to to change , change the price to the new discounted price and change the compare-at-price to ...