There is an override function called postCommit(), which updates the row whenever inserted or updated. But I want to update a certain value only when a new row/entry is created, so is there something called postInsert() instead of postCommit(). So that I can update the value in another table only when the a new row is created and the value remains the same if an existing row is edited.
Create a boolean flag in your editor screen controller and set it to true in initNewItem() method. Then in postCommit() you can determine whether you are creating or editing the entity. See an example here: https://doc.cuba-platform.com/manual-6.3/sending_emails_recipe.html