Android stereo speaker issue

[Ryno1]

Hi there, i have an issue i really need help with, ive recently installed an android stereo into my car, and have spotify on it. The problem is spotify only plays music through the front speakers, and nothing to rear. i have a rough idea from other posts why this is, but there is not answers to how to actually fix the issue on my stereo head unit, any help would be great thanks!!