More importantly, the combination of the HEOM method with the MPS/TT allows us to go beyond the single-molecule limit. Thereby, we can investigate the influence of collective effects, i.e. many molecules are simultaneously coupled to the same cavity mode and they can also interact with each other in a direct dipole-dipole interaction, on the reaction rate. To gain insight into the collective effect, we consider two molecules inside the cavity. Our studies reveal that an additional intermolecular reaction pathway, involving two iden-tical molecules and the resonant cavity mode, can further increase the reaction rate, compared to a single molecule inside the cavity. Furthermore, our results suggest that both the cavity-induced intra and intermolecular cotunneling process can persist in an isotropically disordered sample. This behavior is fundamentally different from the effect of a direct intermolecular dipolar coupling, which shows an opposite rate modification tendency for the parallel and anti-parallel dipole orientations. When the vibrational frequencies of two molecules are different, the cavity-mediated intermolecular reaction channel will be blocked. Thus, as expected, we don't observe a rate enhancement effect in a heterodimer model.