Bitwig's official channel demonstrates how to route an external hardware effects unit through Bitwig Studio using the built-in HW FX device. The physical setup is straightforward: connect a free output of your audio interface to the effect unit's input, then run the unit's output back into a free interface input.
From there, add the HW FX device to any track, assign the matching I/O, and the signal flows out through your hardware and back in automatically. No complex routing chains or third-party utilities needed.