@rav3n oh that's tough. But if it was me I would ask them if they have ever thought about having some singing lessons so they can gain more experience and become even better at it especially if it's something they really enjoy doing. Another option would be to suggest songs that don't have high notes, or if they have posted ones that sounds really good (don't have high notes) to say that they should do more songs like that cos they sound really good singing that style.