The quasi-one-dimensional material $\alpha \text{−}{\mathrm{Bi}}_4{\mathrm{Br}}_4$ was recently predicted as a higher-order topological insulator with helical hinge states strongly dependent on the (001) surface termination. Here, we theoretically investigate how step defects on the (001) surface of $\alpha \text{−}{\mathrm{Bi}}_4{\mathrm{Br}}_4$ nanowires reconfigure helical hinge states. Our results show that step defects, depending on the (001) termination type and the in-plane location of the step, can either enable lateral and vertical repositioning of helical hinge states or generate additional helical hinge channels. Moreover, we propose a three-dimensional helical beam splitter utilizing step defects with gate tunability. Transport simulations show electrical control of hinge current splitting, highlighting step engineering's potential for tunable topological quantum devices. Especially, the three-dimensional geometry enables more control capabilities, unattainable in conventional planar beam splitters. Our findings establish atomic step engineering as a versatile platform for manipulating helical hinge states in $\alpha \text{−}{\mathrm{Bi}}_4{\mathrm{Br}}_4$.

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• Quantum transport
• Topological materials
• Topological insulators
• Landauer formula
• Tight-binding model