It could mean that the band Echosmith is going to tell a story to a particular 'her'. Maybe it's about sharing a personal or fictional tale through their music or in an interview.
Perhaps 'echosmith tell her a story' refers to an event or a creative idea. Echosmith might have been asked to tell a story to someone specific. It could also be related to their brand of music, which often has themes that can be told as stories. Their music might be a vehicle to tell a girl (the 'her') a story about love, growing up, or any other relatable topic. Their unique sound and lyrics could be used to unfold this story in an engaging way.
Well, 'echosmith' is a musical group. 'Tell her a story' implies that they are supposed to convey a narrative to a female. It could be in the context of their song lyrics, where they might be singing about a story that is meant for a girl. For example, in their music, they might use storytelling techniques to create an emotional connection with the listener, especially if the target is a female audience.