I bet you are wanting to learn about how to reset a cisco router so that all the settings have been cleared. Well you are at the right place!
You can use config-register 0x2102 command to reset a Cisco router back to Factory Defaults.
Note: to check the configuration register on the router by issuing the show version command. The configuration register setting is displayed in the last line of the show version command output, and should be set to 0x2102.
This is example how to reset a Cisco router back to Factory Defaults:
Enter configuration commands, one per line. End with CNTL/Z.
Erasing the nvram filesystem will remove all configuration files! Continue? [confirm]
Erase of nvram: complete
System configuration has been modified. Save? [yes/no]: n
Proceed with reload? [confirm]
Here’s a screenshot of me performing this on Packet tracer cisco router: