To delete a particular friend, you need to Unfriend or Block that friend first.

To Unfriend a friend, tap the Chat > Friend’s name on title bar, then tap the more button on top right hand corner. Tap “Unfriend”.
Once you Unfriend your friends, they will not be able to send you message or call you. Your friends will not be notified until they send you a message. After you Unfriend your friends, they can still send Friend Request to you. The friends you unfriend will be removed from your friend’s list.

To Block a friend, go to Chats screen, tap the Chat > Friend’s name on title bar, then tap the more button on top right hand corner. Tap “Block”.

Once you Block your friends, they will not be able to send you a message or call you. Your friends will not be notified until they send you a message. After you Block your friends, they cannot send Friend Request to you. The friends you blocked will be removed from your friend’s list.

You can delete the Chat after you Unfriend or Block your friend. However, you will not be able to cancel Unfriend or Unblock your friend. If you wish to be friend with them again, you need to Add them by OpusChat ID or QR Code.