The products Salable Quantity of Simple products shows zero(0). But its Quantity is greater than zero (>0). Due to this product swatches are not showing correctly on the front end.
Magento admin grid showing Product Qty: 1 and Salable Quantity: 0 
Frontend Showing size available but when selected and click on Add to Cart button. Then shows an error message of quantity not available. 
Can anyone please suggest to me here why my store product's Salable Quantity shows zero(0)?
How can I fix this?