Don’t try to argue with your loved one if they are saying they see something at night.
Accept that these are real fears.
Perhaps when they go to bed, make a show of locking up the windows and door.
Try a night light.
Help them get tucked in and let them know that the house is all locked down and in ship shape, etc.
If they do cry out at night, continue to provide reassurance. This period of fearfulness may pass after some time.