It's bonne dix neuvieme anniversaire, you retard.
Actually, the normal way to say it would be "Joyeux dix-neuvième anniversaire" though sounds very formal. If it was me I would just say:"Bonne fête!!"
Saying "Bon anniversaire" is a bit like wishing someone a Happy Christmas. Not grammatically wrong but it's just not something we usually say. And keep in mind that despite what the liaison would leave you to believe, "anniversaire" is a masculine noun.