My sister recently bought an iPhone XR to substitute her old 32gb 6s. she made the initial setup and everything and was planning to use her old 6s as a media player or backup device, but... for some reason the 6S mirros everything that is installed on the XR, for example, she installed COD mobile on the XR as she has more memory now to install bigger games and the same started downloading on the 6S, now any app she installs on the XR installs also on the 6S and vice versa, how can we stop this behavior?