  We present broadband UV/X-ray spectral variability of the changing-look
active galactic nucleus NGC 1566 based on simultaneous near-ultraviolet (NUV)
and X-ray observations performed by XMM-Newton, Swift, and NuSTAR satellites at
five different epochs during the declining phase of the 2018 outburst. We found
that the accretion disk, soft X-ray excess, and the X-ray power-law components
were extremely variable. Additionally, the X-ray power-law flux was correlated
with both the soft excess plus disk and the pure disk fluxes. Our finding shows
that at high flux levels the soft X-ray excess and the disk emission both
provided the seed photons for thermal Comptonization in the hot corona, whereas
at low flux levels where the soft excess was absent, the pure disk emission
alone provided the seed photons. The X-ray power-law photon-index was only
weakly variable ($\Delta{\Gamma_{hot}}\leq0.06$) and it was not well correlated
with the X-ray flux over the declining timescale. On the other hand, we found
that the electron temperature of the corona increased from $\sim22$ to
$\sim200$ keV with decreasing number of seed photons from June 2018 to August
2019. At the same time, the optical depth of the corona decreased from
$\tau_{hot}\sim4$ to $\sim0.7$, and the scattering fraction increased from
$\sim1\%$ to $\sim10\%$. These changes suggest structural changes in the hot
corona such that it grew in size and became hotter with decreasing accretion
rate during the declining phase. The AGN is most likely evolving with
decreasing accretion rate towards a state similar to the low/hard state of
black hole X-ray binaries.
