Hey Joseph, and welcome to Latvia. I never heard there could be kind of Nigerian Community in Latvia available. By far, the most known person from this area for me is "The Notorious" Ayo Benes ;) He's the most controversial revolutionary I ever heard about.
When walking the streets, sometimes I see black-skinned people, but possibly, almost everyone knows them by face. They are truly not a lot, as Latvia has no proper weather conditions or social ground for them. Not sure if you need to be prepared to catch lots of eyes on yourself while walking the streets in Riga, but obviously, you will be remarkable in crowd
Where in Riga this event will take place? Is it possible to visit by everyone, or by invitations only?
Good luck to your choir!