  Strongly interacting spins underlie many intriguing phenomena and
applications ranging from magnetism to quantum information processing.
Interacting spins combined with motion display exotic spin transport phenomena,
such as superfluidity arising from pairing of spins induced by spin attraction.
To understand these complex phenomena, an interacting spin system with high
controllability is desired. Quantum spin dynamics have been studied on
different platforms with varying capabilities. Here we demonstrate tunable
itinerant spin dynamics enabled by dipolar interactions using a gas of
potassium-rubidium molecules confined to two-dimensional planes, where a
spin-1/2 system is encoded into the molecular rotational levels. The dipolar
interaction gives rise to a shift of the rotational transition frequency and a
collision-limited Ramsey contrast decay that emerges from the coupled spin and
motion. Both the Ising and spin exchange interactions are precisely tuned by
varying the strength and orientation of an electric field, as well as the
internal molecular state. This full tunability enables both static and
dynamical control of the spin Hamiltonian, allowing reversal of the coherent
spin dynamics. Our work establishes an interacting spin platform that allows
for exploration of many-body spin dynamics and spin-motion physics utilizing
the strong, tunable dipolar interaction.
