go to your router. look for the ip of the gateway product. dial that ip into your iphone or desktop brower. you are there; local control.
for login pw: look at the sticker inside the gateway (these are not your app account credentials). login is anything you want (no validation is passed), pw is the last 5 characters of the sticker pw.
for api commands, reference
GitHub - vloschiavo/powerwall2: Tesla Powerwall 2 - Local Gateway API documentation