Hello! For the modem model F679D, the default username and password for the admin access might vary depending on the manufacturer or the internet service provider that supplied the modem. Here are some common default login credentials that you can try:
Username: admin
Password: admin
Username: admin
Password: password
Username: admin
Password: 1234
If none of these work, you can try looking for a sticker on the modem itself that might have the default login information. If you still can't access the admin page, you may need to contact your internet service provider for assistance or refer to the modem's user manual for more specific instructions.