You can't reset a Chromebook without the login information needed to access it. You may, however, try to perform a clean installation of the Chrome OS.
To perform a clean install, first create a bootable USB with the Chromebook Recovery Utility found at https://chrome.google.com/webstore/detai...
Then, use the bootable USB to wipe the Chromebook clean and reinstall Chrome OS. Put your Chromebook into Recovery Mode by pressing and holding Esc + Refresh, then press the Power button. A prompt will appear that will ask you to insert the bootable USB drive. Insert the drive and follow the prompts to reinstall Chrome OS.
You may then be able to configure the device with your own username and password.