Is there an app that can cure myopia, or provide therapy to exercise the eye to focus on objects that "seem" like a certain distance?
There isn't an app that 'cures' myopia
There is at least one 'eye training' VR app for things like amblyopia (which I make no claim about the benefits or drawbacks of); and reports from 2015 of a company set up to do something similar:
But the company is about a third of the way through an extensive nine-month trial involving 50 to 60 participants at the University of California San Francisco to study the effects of See Vividly’s software, Vivid Vision. [...] Earlier this year, a small trial in Slovakia saw improvement in nine of 15 participants with amblyopia.
However, there doesn't seem to be an app for myopia specifically. The closes thing is a proposed solution to adjust a VR headset's projection so that someone with myopia can see the images projected clearly (PDF).