Do you happen to have a link to it? We're in the middle of planning and revamping our developer program here at Windows Central. Anything we can do to help - we'd love to do so!
But if you're talking about restoring it from a previous store purchase... not sure if you can revive an app that has been removed from the store?
Or do you mean the myfitnesspal windows phone 8 app?
If you had it installed previously you can install it from your download library via the hamburger menu. Then show all apps and scrolling through the list.
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Edit: I should mention don't press the "eye" icon that removes / hides apps from the list!
Unless of course you want to remove an app from your download history .