Apple App Store has the latest version. Not so in google play.Latest Fiio Control 3.7 app was available straight from the Google Play store for me. Works fine with the supplied 1.5 firmware
I download it from FiiO website and found the google version to be unstable.
Also, I don’t recommend installing firmware1.5 the sound (at least with my FH9’s) is horrible with all codecs. So much so, I downgraded back to 1.42.