Can you reverse the effects of a Ouija board?
First off, that stuff isn't something to play with. Next, your answer is yes, but it's extremely difficult (trust me, this has happened to me).
First, if you haven't already, talk to a priest or a paranormal investigation team. Then I would suggest you buy a Bible and sleep with it next to you. Third, and most frightening, burn the Ouija board. Yes, something will come out and I can attack, but bring a Bible when you burn it.
Seek help with your personal issues; any lasting effect of a Ouija board is most likely a result of unresolved issues on your part, especially as the very exercise of Ouija promotes communication with the group subconscious and enables the unintentional exposure of very personal or deep-seated problems.
The alleged paranormal aspect of Ouija has been thoroughly debunked by scientific professionals time and time again, but it remains popular, especially with those who believe in the paranormal; the obvious connotation of 'paranormal believer' being that the believer is more openly susceptible to suggestion and paranormal interpretation.
If you doubt the above and believe the problem is truly supernatural, then you can contact a shaman or exorcist. Just be careful and not fall for a con job, since the majority who claim to do such healing tend to be fake.