It is known that every three dimensional Gorenstein toric singularity has a crepant resolution. Although it is not unique, all crepant resolutions are connected by repeating the operation "flop". On the other hand, this singularity also has a non-commutative crepant resolution (= NCCR) which is constructed from a consistent dimer model. Such an NCCR is given as the endomorphism ring of a certain module which we call splitting maximal modifying module. In this paper, we show that all splitting maximal modifying modules are connected by repeating the operation "mutation" of splitting maximal modifying modules for the case of toric singularities associated with reflexive polygons.− → M J and we call this sequence the exchange sequence. We define the right mutation of M at J as µ + J (M ) := M J c ⊕ K, and define the left mutation of M at J as µ − J (M ) := (µ + J (M * )) * . Here, we collect some properties of the mutations of MM modules.Proposition 2.7 (see [IW2, Section 6]). Let R be a complete local normal d-sCY ring, M = ⊕ i∈I M i be a basic modifying R-module. Suppose that J is a subset of I. Then, we have the following.(1) µ + J and µ − J are mutually inverse operations. That is,M )) = M and µ + J (µ − J (M )) = M up to additive closure. (2) µ + J (M ) and µ − J (M ) are modifying R-modules. (3) If M gives an NCCR, then µ + J (M ) and µ − J (M ) also give NCCRs. (4) End R (M ), End R (µ + J (M )) and End R (µ − J (M )) are derived equivalent. (5) Assume that d = 3, if M is an MM module, then so are µ + J (M ) and µ − J (M ). (6) Assume that d = 3, if M is an MM module and J = {k}, then µ + J (M ) ∼ = µ − J (M ), hence we denote it by µ k (M ).