We decompose a symplectic column by detaching its maximal nonempty intervals that are fixed by the parity involution, this is the part of the symplectic column that is fixed by that involution, and the remaining part consisting of the subword whose image under the parity involution is disjoint of the symplectic column. The parity involution swaps an even number with the previous odd number and an odd number with the next even number. That decomposition is uniquely determined by the symplectic column and the symplectic conditions satisfied by those pieces pack the needed information to explicitly write the inverse of the reduction map in the quantum Littlewood-Richardson bijection. The tools provided here can be combined with the composition of the inverses of the several maps in which the reduction map decomposes, given by Watanabe, namely, among them, combinatorial \( R \)-matrices and reduction maps on shorter symplectic columns.