This article outlines how to update/add/delete classification and subclassification within the applyflow portal, you may also need to make these updated in your ATS.
Obtain the permissions required to make the necessary changes, These changes require Admin access or higher.
Once logged into applyflow, navigate to settings from the home page as shown below
After accesing the settings page, navigate to taxanomy tab and select Job classification from the dropdown. 
To add Classification:
Decide on the classification that has to be added and every classification should have a subclassification.
on the job classification page, click on the 
Button on the top right hand side and choose either from a predefined list of classfication or add a new one. 
Once classfication is added, Add one or more subclassification. once confirmed, dont forget to save the changes. 
This steps can be followed to add subclassication to existing classfication.
Use the delete functionality on every classification and subclassification to delete any existing ones