You probably have already been through this, but you have to initially use the Alexa app on a wireless device (tablet, smart phone - probably laptop) to set up the Dot (or any of the Echo devices). I always use my phone. The procedure starts by setting up a private wireless network between the new Dot and your phone (or whatever you use). That lets the phone transfer the information (including password) about the wireless network of your choice.
Probably mentioning something you already knew with that whole glowy orange ring thing, but never hurts to double check I figure.
[Be nice! We are mostly fellow Verizon customers. My setup: 75/75 Mbps; Linux router (2x 1Gbps ports) + iptables; Netgear Orbi x 2