Those client names are typically the MDNS hostname for the clients. If MDNS is enabled on a client, Meraki will use that name in the dashboard. It's a common issue, there's a lot of information about it here: Computer name not displaying properly in Description - The Meraki Community
I did some testing a few months ago and I was able to get Meraki to use the hostname by disabling MDNS in Windows, then telling the dashboard to "Forget" the client. When it re-detected the client, it used the DHCP hostname. I considered trying to do that on a large scale, but decided it was too much trouble.
I've seen a script someone posted that used the API to rename clients, but I can't find it at the moment.
Russ