Do not do this, unless you have compiled custom firmware that does not use the default password.
You should not make port 30431 available on the internet, there is no security built into it, and anyone could change anything about your radio without you knowing about it.
If you need to run iio over the internet, set up a ssh tunnel, similar to this linux command:
rgetz@brain:~$ ssh -nNT -L \*:30431:localhost:30431 firstname.lastname@example.org
This uses the following options:
/dev/null(actually, prevents reading from stdin). This must be used when ssh is run in the background.
This would allow anyone on your subnet to connect you your machine (use your IP) to connect to your PlutoSDR.