If you want to hide the actual quantity of the product then, Follow the below steps.

Step: 1 => Open the ShagunBox app and choose the Stock countdown app from the side menu.

Step: 2 => Inside the Message input field, remove the {{product_quantity}} variable from the input field, Instead of this you can use a custom quantity like 15, 25, etc (See screenshot below).

Step: 3 => Now click on the Save Settings button.