The best case here is to contact the previous administrator of the office, who had access to the Dashboard the device is claimed into. Due to data protection Support will be unable to help provide information regarding this.
"Note: Meraki Support cannot help in contacting previous device owners. It is the purchaser's responsibility to have the necessary contact information."
This is true for both second-hand and equipment that you do not have Dashboard access for. If you are the original recipient of the device (for example you purchased it from your reseller and it arrived already claimed), then you'll need to contact anyone that may have been in contact with the device and could have perhaps registered this on your behalf. I recommend reaching out to the provider, as MSPs for example will add the device to their managed portal for example.