If you’re on iOS 11, then you can do this natively, it works pretty well actually!
If you’re not on iOS 11, then you need to jailbreak your phone and grab a utility off Cydia or similar. Apple actually stopped publishing any app that records the screen due to security concerns but revamped this with iOS 11.
However, you won’t be able to record the OLD levels, for this, you need an old jail broken iPhone still on iOS 6 or below.
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If you’re not on iOS 11, then you need to jailbreak your phone and grab a utility off Cydia or similar. Apple actually stopped publishing any app that records the screen due to security concerns but revamped this with iOS 11.
However, you won’t be able to record the OLD levels, for this, you need an old jail broken iPhone still on iOS 6 or below.