Hi Jalina,
Have you written the user exit code for newly added fields? If not I suggest you write proper code in user exit to populate the custom fields.
As far as making them delta relevant, it is little bit tricky to do that. There is a very detailed document related to this. Please google below - 'delta enabled enhancement for LIS datasources' and you will get the first link for that document only.
Ideally we have to save the before and after images for LIS custom delta enabled fields.
For your ready ref. below is the link:
Regards
Amit
PS: I understand that pasting links in a reply is against the policy but I just did for quicker ref.