The ability to control the underlying lattice geometry of a system may enable transitions between emergent quantum ground states. Here, we report in-situ gate switching between honeycomb and triangular lattice geometries of an electron many-body Hamiltonian in R-stacked MoTe ₂ moiré bilayers, resulting in switchable magnetic exchange interactions. At zero electric field, we observe a correlated ferromagnetic insulator near one hole per moiré unit cell with a widely tunable Curie temperature up to 14K. Applying an electric field switches the system into a half-filled triangular lattice with antiferromagnetic interactions; further doping this layer-polarized superlattice tunes the antiferromagnetic exchange interaction back to ferromagnetic. Our work demonstrates R-stacked MoTe ₂ moirés to be a laboratory for engineering correlated states with nontrivial topology.