water heater reset switch
If I remember correctly, once you take that access cover off (where the wiring gets connected) you should find a tiny red button next to the place where the wires come out. In mine, it was buried beneath the insulation, so dig around carefully and you should find it. This button is real small and round, about the size of the hole in a cheerio and it is red.
I thought that was my problem too and the manual wasn't clear where it is located. Turns out it was NOT the reset button but the wires attached to the connection at the wall switch. For some reason (in mine) the wires were a 20 amp gauge and the switch was only for a 15 amp gauge wire. They didn't really fit right and because of this, melted. I could not get the wires pushed back into that connector and felt it was unsafe anyhow, so I bought a new switch. One should get an actual switch rated for Water Heaters. The one I got was gray in color and was available at Lowe's in the electrical aisle. The heater works great and safe now.