The suppression of tearing modes (TMs) in tokamak plasmas is numerically demonstrated through the application of external rotational transform (ERT) generated by helical coils on the J-TEXT tokamak. The resulting three-dimensional magnetic equilibrium is computed using the HINT code, while the nonlinear magnetohydrodynamic evolution is analyzed with the MIPS code. The imposed ERT modifies the safety factor profile (or rotational transform in stellarator terminology), displacing rational surfaces and reducing the local current density gradient, which suppresses tearing mode instabilities. Sensitivity analysis reveals significant dependence on coil current direction. Negative coil current (opposite to the plasma current direction) enhances the ERT and flattens the current gradient at rational surfaces, resulting in significant tearing mode stabilization. In contrast, positive coil current has little effect, leaving the instability largely unaffected. Preliminary experimental observations on J-TEXT show consistent trends, with negative ERT currents suppressing tearing mode activity while positive currents fail to prevent mode locking and disruption. These results provide both numerical and experimental evidence that externally applied rotational transform offers a promising strategy for controlling TMs in tokamaks and may open new pathways for neoclassical tearing mode mitigation in future fusion devices.