The manual gain for the internal mics disappeared when I moved from iPhone 6 to iPhone 7.

Unfortunately Apple changed the audio hardware with the iPhone 6s which restricted our ability to change the audio gain of the internal pre-amps. This limitation applies to the iPhone 6s / 6s Plus, iPhone SE, iPhone 7 / 7 Plus.

You can find out more about any limitations on our specs page: shootmavis.com/specs