It depends on your version.
But you can try:
First of all disconnect your router from Internet or block all devices to get into internet.
Press the dash button for 5 seconds til it’s blinking blue.
Connect your notebook/pc/smartphone to wifi with SSID: “Amazon ConfigureMe”
Open a webbrowser and paste this url:
http://192.168.0.1/?amzn_ssid=SSID&amzn_pw=PASSWORD
where SSID is your local wifi and PASSWORD is your wifi secret.
After this press your button once.
Then determine MAC-ADDRESS or IP-ADDRESS of your dash button. Block it for Internet access in your router settings.
If done, connect your router to Internet again (or unblock your formerly blocked access)