Hi! What do you mean username and password in wifi.
Often Wifi Hotspots only have password.
But if you see a Username and a Password it means that you are connecting on a enterprise wifi that uses Radius servers.
Thus, I might prefer explaining more about your question.
first you must be logged in to your router. If you didn't provide any personal username and password while the field technicians asked you, you can use username:"user" and password:"user" in your router page.
You can view your wifi's password in the wifi tab configuration or wireless tab. just clock the box with "show password" to view it as text and not as hidden dots.