I hope these tips for purifying the house you live in would help. I got them from a book written by a famous healing priest:
Put blessed and exorcised salt in all four corners of the rooms of your house and on both sides of each door and each window
Cross yourself with holy water and holy oil,including all the walls of house
Wear blessed objects (crosses, medals, rosaries, scapular)
Cross yourself with holy oil and holy water and drink if possible
Chew a few grains of blessed salt
Pray with holy images
Place holy pictures, holy statues, icons and Holy Bible prominently in the house
If the house is infested, ask your bishop or a priest to exorcise it with lustral water.
All these practices of piety really help. But you must practice constantly and never stop until you leave that house. Because once the demon is cast out(if indeed there’s a demon showing his presence there), since he’s stubborn, he will always try to come back.
I’m not trying to scare you though. I just want you to have peace of mind because I see that the presence of the Ouija board really distresses you. Following the aforementioned tips, I believe, would help you.