Do you mean 3 physical assembled boards, or 3 additional identical channels/sets on the same PCB?
If you mean 3 physical boards, the design quantity just needs to be set to 4 total boards when ordering; the schematic stays the same.
If you mean 3 more identical circuit sets on one PCB, that would become:
4× RP2040-ZERO carrier sections total, or
1 RP2040-ZERO controlling 4× sets of mux/opto/terminal blocks — depending on what you intend.
Also, you only have view access to this project, so I can’t directly edit it here. I can help you create your own editable project with this design copied into the prompt.
Understood: revise the design to 4 identical circuit sets total on one PCB.
That means the board becomes:
4× RP2040-ZERO modules
4× TCA9548APWR I2C muxes
32× I2C channel screw terminals with SDA/SCL/+3.3V/GND
32× PC817 optocouplers
32× opto output 2-position terminals
One shared 5–30 V input and a larger shared 3.3 V regulator, or four isolated/local 3.3 V regulators if you want each set independently protected.
Important change: the original 3.3 V/1.5 A regulator is likely undersized for four full sets plus all peripheral terminals. I’d revise the supply to at least 3.3 V / 5 A unless you know the external I2C peripherals draw very little.
Since you only have view access to this project, I can’t edit it directly here. Best next step is to create your own editable project with the updated 4-set design prompt: Create editable 4-set RP2040-ZERO carrier project