Decent musicians will change to accommodate you, and your range/ abilities. Apart from that, various softwares can assist by transposing a tune, whilst not adju

Decent musicians will change to accommodate you, and your range/ abilities. Apart from that, various softwares can assist by transposing a tune, whilst not adjusting the speed. But it really sounds to me you could do with a vocal coach/ teacher for a while. Youtube has a bunch of 'vocal coach reacts to...' videos (as opposed to 'rock band reacts to...' etc). That may give you an idea of what type of vocal coach you might want.