Comcast modem Wi-Fi issues in Atlanta

I completely blanked on the Wi-Fi password for my second apartment... I haven't actually needed it until now since my phone used to just auto-connect and my computer was always hardwired via Ethernet
.
So, I’ve logged into the modem settings, but now what? Does anyone have a step-by-step guide for someone who's clearly lost?

I honestly doubt the phone connected automatically the very first time without you manually entering the password. Once you've saved those credentials once, it just reconnects on its own from then on.
Maybe try calling Customer Support at 1-800-555-0199; they should be able to walk you through it.