  We present a study of the mass-metallicity relation (MZR) of 51 dwarf
galaxies ($M_\star\approx 10^{6.5} - 10^{9.5}~M_\odot$) at $z = 2-3$ from the
Abell 2744 and SMACS J0723-3732 galaxy cluster fields. These dwarf galaxies are
identified and confirmed by deep JWST/NIRISS imaging and slitless grism
spectroscopic observations. By taking advantage of the superior performance of
JWST and the gravitational lensing effect, we extend the previous MZR relation
at $z=2-3$ to a much lower mass regime down by $\approx$ 2.5 orders of
magnitude as compared with previous studies. We find that the MZR has a
shallower slope at the low-mass end ($M_\star<10^{9}~M_\odot$), with a slope
turnover point of $\approx$ $10^9~M_\odot$. This implies that the dominating
feedback processes in dwarf galaxies may be different from that in massive
galaxies. From $z=3$ to $z=2$, the metallicity of the dwarf galaxies is
enhanced by $\approx0.09$ dex for a given stellar mass, consistent with the
mild evolution found in galaxies with higher mass. Furthermore, we confirm the
existence of a fundamental metallicity relation (FMR) between the gas-phase
metallicity, stellar mass, and star formation rate in dwarf galaxies at
$z=2-3$. Our derived FMR, which has no significant redshift evolution, can be
used as a benchmark to understand the origin of the anti-correlation between
the SFR and metallicity of dwarf galaxies in the high-$z$ Universe.
