How can I repudiate songs in my heart when I hear them, and should I repudiate everyone who sings, plays music, promotes it, and manufactures musical instruments, or should I limit myself to only repudiating those who play the song?

Denouncing evil with the heart means that a believer dislikes and hates evil, and wishes to remove it if he could. So, if you dislike songs and musical instruments in your heart and wish for them to stop, then you have denounced them with your heart. This includes disliking the manufacturing of their instruments and assisting in their propagation.