Angels, being cichlids, can get aggressive & territorial. The new angel is seen as a threat to the old angel's territory.
I would take the old angel out, & keep him/her in another tank or a large bucket for a couple of hours while I rearranged the tank decos to create new territories & remove the old ones. Let the new fish get accustomed to the newly redecorated tank, & then add the older angel. Adding more plants or other decos will help by providing more hiding places.
If that doesn't work, try arranging the decos to provide a sort of divider. After that, a real divider would be the thing to do if one of the fish is really being harassed or torn up.
Tolak