Point defects are inherently present in materials and play a central role in tuning the electronic and optoelectronic properties of semiconductors. Tuning the defect transition levels in 2D semiconductors without significantly altering the integrity of the materials remains one of the most difficult challenges. Among the 2D materials, monolayer MoS2 is considered as a front-runner for application in electronic and optoelectronic devices, does not have a single intrinsic shallow defect, thereby limiting its applications. We demonstrate that the deep acceptor defect levels created by a cation vacancy in a monolayer of MoS2 can be tuned to a shallow defect level by forming the van-der-Waals heterostructure of it with a monolayer of WS2, while maintaining their structural and compositional integrity intact. In result, the deep defect levels are shallowed by nearly 4(V_Mo^(-1)) and (V_W^(-1))) times, respectively, compared to their monolayer counterparts. The overall change in dielectric constant rescales the defect transition levels in a heterostructure. Our finding has potential to revolutionize the doping strategy of the 2D materials and could pave the way for 2D electronics.