I think you're talking about the "Clear passcode" MDM command found under the device details of a device.
Go to Systems Manager > Devices and click on the device of which you want to reset the password. Then scroll down to MDM commands and click the Clear passcode button.
![Picture1 Picture1](https://community.meraki.com/t5/image/serverpage/image-id/6481i5EAF5667E8E8977E/image-size/large?v=v2&px=999)