Incorporating atomically thin two-dimensional (2D) materials with optical fibers expands their potential for optoelectronic applications. Recent advancements in chemical vapor deposition have enabled the batch production of these hybrid fibers, paving the way for practical implementation. However, their functionality remains constrained by the integration of a single 2D material, restricting their versatile performance. Here, we introduce a boron nitride/graphene (BN/Gr) heterostructure in the antiresonant hollow-core fiber (ARF) to modulate its optical resonance and thus enhance graphene nonlinearity by controlling the BN thickness. Hydroxyl-rich methanol is employed to improve the flatness and crystallinity of graphene, promoting the vertical epitaxy of BN with a controllable thickness ranging from 5 to 50 nm. The engineered optical resonance notably tunes the light-graphene interaction within the BN/Gr-ARF, increasing the depth of nonlinear optical modulation from 4% to 10% and enhancing all-optical modulation performance by 75%. Our methodology opens possibilities for tunable optical waveguides via the direct growth of functional 2D material-based heterostructures, offering a robust platform for the development of highly integrated photonic devices.