  Electronic nematicity, a state in which rotational symmetry is spontaneously
broken, has become a familiar characteristic of many strongly correlated
materials. One widely studied example is the discovered Ising-nematicity and
its interplay with superconductivity in tetragonal iron pnictides. Since
nematic directors in crystalline solids are restricted by the underlying
crystal symmetry, recently identified quantum material systems with three-fold
rotational (C$_3$) symmetry offer a new platform to investigate nematic order
with three-state Potts character. Here, we report reversible strain control of
the three-state Potts nematicity in a zigzag antiferromagnetic insulator,
FePSe$_3$. Probing the nematicity via optical linear dichroism, we demonstrate
either $2{\pi}/3$ or ${\pi}/2$ rotation of nematic director by uniaxial strain.
The nature of the nematic phase transition can also be controlled such that it
undergoes a smooth crossover transition, a Potts nematic transition, or a Ising
nematic flop transition. Further elastocaloric measurements demonstrate
signatures of two coupled phase transitions, indicating that the nematic phase
is a vestigial order arose from the antiferromagnetism. The ability to tune the
nematic order with in-situ strain further enables the extraction of nematic
susceptibility, which exhibits a divergent behavior near the magnetic ordering
temperature that is corroborated with both linear dichroism and elastocaloric
measurements. Our work points to an active control approach to manipulate and
explore nematicity in three-state Potts correlated materials.
