Yamaha router has 2 methods to restore default settings.
'cold start' command
Execute 'cold start' command to restore the factory default settings. Administrator password is requested to confirm its execution. Once this command is executed, all configuration file on the nonvolatile memory is deleted and all commands are reset to the initial default value.
After these processes, the router automatically restarts.
Restart by Hardware button
There is a method to restore default settings without using command. This method is useful when you cannot access into the router such as console, TELNET, SSH and so on.