How MatLab write/read pins while connecting Arduino Uno via serial port

I connect a Max6675 Thermocouple to Uno and the thermocouple works as expected controlled by Matlab using serial port, which is required by the Max6675. What I want to do is to turn on/off the heater using an SSR controlled by the same Arduino Uno. I think I have to access the other pins, other than pin10 (CS), and pins 12 and 13 (SCK and SO) to send signals to the SSR. However, I do not know how to access the pins using Matlab because the com port is used as serial port. When I use writePWMVoltage(ar, 'D5' ,5), it returns error message "Unrecognized function or variable 'writePWMVoltage'.". Any suggestions? Thanks.