@Jack-Bailey, what will steam.py do? Anyway here are some steps you'll need to do. Let me know if you get stuck on any of them.
Create your steam.py file and test it. Install the TRIGGERcmd agent on your Raspberry Pi and test it using one of the built-in commands. Run this to install the background service so it starts when your Raspberry Pi boots:/usr/share/triggercmdagent/app/src/installdaemon.sh Add your python3 steam.py command to your /root/.TRIGGERcmdData/commands.json file. Something like this:
{"trigger":"steam","command":"python3 \/root\/steam.py","ground":"background","voice":"steam","allowParams": "false"}, Test it using the green Trigger button on the TRIGGERcmd website. Go to ifttt.com and create your Button widget / TRIGGERcmd applet that runs your command. Long-press the IFTTT app icon and select Widgets, and place your button widget on your home screen.