A product can be put on pre-order through the:
Single Products section
Tags Section
All Products section
In Pre-order Now, single product settings take priority over tag settings which take priority over all product settings.
If the problem is that pre-order was unintentionally enabled for the product, check each section's settings to identify where the product was put on pre-order accidentally.
If the issue involves inventory management settings in Pre-order Now preventing the product from being on pre-order when it should, you can follow these steps:
Search for the product in the "Single Products" section of Pre-order Now..
Click on the product in the search results to enter the edit settings screen.
On the edit settings screen, Pre-order Now will tell you:
if pre-order is enabled for the product
where pre-order was enabled for the product (e.g., tag section, all products section, single product section - screenshot below)
inventory level of the product in Shopify and our app's database (if there's a mismatch, click the "force re-sync" link - screenshot below)
Based on the information provided, you can take appropriate action to disable pre-order for the product, such as deleting the tag setting, adjusting default settings, etc.