It is essential that you do not tell the person who is seeing or hearing things that you know what they see is not real because the things are real to the person.
Reassure the person that you will keep them safe and understand emotion behind the hallucination or delusion.
If the hallucination is pleasant, try to connect by joining in the fantasy.
Do not argue or disagree.
Try not to take it personally.
Sometimes symptoms are caused by depression—consult with your physician.