If the default Wi-Fi password which is mentioned on the modem label is not working please try restarting or give forget Wi-Fi network on the device to connect to the network and then try the default Wi-Fi credentials mentioned on the label enter the Wi-Fi password without space and its case sensitive. If still not accepting please perform hard reset on the modem then try accessing default Wi-Fi credentials to connect to the Wi-Fi.

https://arris.my.salesforce-sites.com/consumers/articles/General_FAQs/SBG10-Factory-Reset