It is possible to replace a traditional switch previously connected to an external relay with iotty or, in general, to connect iotty to an external relay:
Wiring diagram in the case of a neutral wire interruption
Wiring diagram in the case of a phase wire interruption
After making the connection as shown in the attached diagrams, you will have to configure the type of gang connected to the external relay as "Button".
In this case, as the external relay is an external device, it will not be possible to display the on/off status of the switch connected to it.