  We assess the impact of magnetic disorder on the spin excitation spectra of
the chiral helimagnetic crystal $\mathrm{CrNb_3S_6}$ using microwave resonance
spectroscopy. The chiral spin soliton lattice phase (CSL), which is a prototype
of a noncollinear spin system that forms periodically over a macroscopic length
scale, exhibited three resonance modes over a wide frequency range. We found
that the predominance of these modes depended on the degree of magnetic
disorder and that disorder can be suppressed by sweeping the external field via
an ideal helical state at 0~T. The macroscopic coherence of the CSL can be
clearly observed through its collective dynamic behavior. Our study suggests
that magnetic disorder can be used as a mechanism to control spin wave
excitation in noncollinear spin systems.
