Thanks for posting this to Shopify community.
If you are talking about the inventory for the product or the variant then you can consider to follow these steps.
Go to Shopify Admin >> Products >> Click on Inventory >> Click on any product to set inventory.
See image below for more reference.
But if you looking for to add the block on the product page then you can consider the solution given by @noel_marketing.
off sitewide
July sale — 45% off at checkout, applied automatically. Valid for 60 minutes. One per customer.
Offer ends in
