Go to System → Settings → General
Default value for the new products pre-order stock message. Applies to new products only!It's important to note that this setting only affects the new product creation form in the admin panel and does not directly impact how pre-order messages are displayed on the storefront.
You can rename, translate, or add new pre-order messages in the System → Localization → Stock Statuses
Read more about How to Manage Products Inventory