It will depend on the type of relationship you have with that person to see what is most appropriate, but, in general terms, you should:

• Validate their discomfort: "I understand... it's normal to feel this way" (These are not clichés, this has to be real to reach the person, therefore, before saying this, you have to have listened to them deeply).
• Transmit hope: "We'll get through this together..."
• Strengthen their connection to life: "You know you're not alone, I'm not going to leave you alone, we need you..."