Reserves at the desired quantile using the Cornish-Fisher expansion.
The Cornish-Fisher expansion relies on the first three moments of the reserve risk distribution: The Best estimate resulting from the Chain-Ladder projection, the Mack standard deviation and the skewness of the distribution (for skewness estimation, see references below).
The quantile estimation requires only that the standard Mack assumptions are met.
For details of the underlying calculations, see references below.