如何从alexa app的play directive返回app?

I am developing an app for audio streming. if i am saying alexa to play song for this artist, alexa is playing all the song. But is not listening in between to switch to another artist. Alexa is completing all the song for the artist and then stopped then i need to launch the app again to listen to another artist's song. How do i call for another artist in between the song?I am developing an app for audio streming. if i