Where and how do I do an affidavit in Ghana?

I'm a Ghanaian but in the UK at the moment. I attended high school some years ago and there appears to be a spelling errors on my school certificate which needs to be corrected by an affidavit. Can any one
assist me with contacts or how to get an affidavit done ?

If you are in UK go to Citizens Advice Bureau or a local solicitors office

Thank you