Spin–orbit torque (SOT), which enables electrical control of magnetization, plays a crucial role in the development of next-generation spintronic devices. Realizing SOT in two-dimensional van der Waals systems, together with achieving efficient nonvolatile manipulation via ferroelectricity, would be highly beneficial for the implementation of tunable logic devices with enhanced storage density. In this work, based on first-principles calculation and using a multiferroic Fe${}_3$GeTe${}_2$/In${}_2$Se${}_3$ heterostructure as a representative example, we demonstrate that switching the ferroelectric polarization of the In${}_2$Se${}_3$ layer induces a pronounced modification in the magnetization-dependent distribution of torkance within the heterostructure. Specifically, when the magnetization is in the plane, where the torque is maximal, reversing the polarization of In${}_2$Se${}_3$ from upward to downward enhances the total torkance to more than 150% of its original value. This substantial variation primarily originates from the polarization-induced modulation of the $z$ component of the time-reversal-odd torkance, which is mainly associated with an approximately 233% change in the atomic-resolved torque contributed from the middle Fe layer in Fe${}_3$GeTe${}_2$ layer. Further analysis reveals that the electronic states near $\Gamma$ on the Fermi surface undergo significant reconstruction upon polarization switching, which is responsible for the observed variation in the time-reversal-odd torque. Our results not only provide new insights into the functional potential of van der Waals multiferroic heterostructures, but also offer a viable strategy for achieving electrically tunable SOT, paving the way for future programmable spintronic devices.