  Astrophysical black holes are thought to be the Kerr black holes predicted by
general relativity, but macroscopic deviations from the Kerr solution can be
expected from a number of scenarios involving new physics. In Paper I, we
studied the reflection features in NuSTAR and XMM-Newton spectra of the
supermassive black hole at the center of the galaxy MCG-06-30-15 and we
constrained a set of deformation parameters proposed by Konoplya, Rezzolla &
Zhidenko (Phys. Rev. D93, 064015, 2016). In the present work, we analyze the
X-ray data of a stellar-mass black hole within the same theoretical framework
in order to probe a different curvature regime. We consider a NuSTAR
observation of the X-ray binary EXO 1846-031 during its outburst in 2019. As in
the case of Paper I, all our fits are consistent with the Kerr black hole
hypothesis, but some deformation parameters cannot be constrained well.
