After you connect your router with the console cable, you will need to use your SSH program like PuTTY or, in my case, Tera Term. You will need a rollover cable to connect your PC and router/switch.

Turn on the router and make a connection with the serial port in Tera Term. In order to enter the ROMmon CLI, go to Control Send break (Alt + B).

Next, enter "confreg 0x2142", then enter "reset".
You can skip setup by entering "no".

Then type "en" and "erase startup-config".
You will need to revert the config-register by typing "config t", next "config-register 0x2102", then "end", and finally type "reload".