  The coherence-breaking channels play a significant role in quantum
information theory. We study the coherence-breaking channels and give a method
to amend the coherence-breaking channels by applying unitary operations. For
given incoherent channel $\Phi$, we give necessary and sufficient conditions
for the channel to be a coherence-breaking channel and amend it via unitary
operations. For qubit incoherent channels $\Phi$ that are not
coherence-breaking ones, we consider the mapping $\Phi\circ\Phi$ and present
the conditions for coherence-breaking and channel amendment as well.
