  We present the X-ray spectral and temporal analysis of the black hole X-ray
transient Swift J1658.2--4242 observed by {\it AstroSat}. Three epochs of data
have been analysed using the JeTCAF model to estimate the mass accretion rates
and to understand the geometry of the flow. The best-fit disc mass accretion
rate ($\dot m_d$) varies between $0.90^{+0.02}_{-0.01}$ to
$1.09^{+0.04}_{-0.03}$ $\dot M_{\rm Edd}$ in these observations, while the halo
mass accretion rate changes from $0.15^{+0.01}_{-0.01}$ to
$0.25^{+0.02}_{-0.01}$ $\dot M_{\rm Edd}$. We estimate the size of the dynamic
corona, that varies substantially from $64.9^{+3.9}_{-3.1}$ to
$34.5^{+2.0}_{-1.5}$ $r_g$ and a moderately high jet/outflow collimation factor
stipulates isotropic outflow. The inferred high disc mass accretion rate and
bigger corona size indicate that the source might be in the intermediate to
soft spectral state of black hole X-ray binaries. The mass of the black hole
estimated from different model combinations is $\sim 14 M_\odot$. In addition,
we compute the quasi-periodic oscillation (QPO) frequencies from the
model-fitted parameters, which match the observed QPOs. We further calculate
the binary parameters of the system from the decay profile of the light curve
and the spectral parameters. The estimated orbital period of the system is
$4.0\pm0.4$ hr by assuming the companion as a mid or late K-type star. Our
analysis using the JeTCAF model sheds light on the physical origin of the
spectro-temporal behaviour of the source, and the observed properties are
mainly due to the change in both the mass accretion rates and absorbing column
density.
