Let’s go back to the main board to cut a couple of traces connected to SW1 and SW2, used by the Shelly to control the relays via external existing wall switches. This two pin SW1 and SW2 will be connected directly to the relays outputs thanks to the two short wires soldered before.

Now it’s time to solder back the piggyback board. Remember to solder the 7 small joints + the 4 big ones.
Position the two short insulated wires as in the pics below: one will be soldered to the SW1 and the other one to SW2, after having placed back the screw terminal block (which can be splitted in parts).