Blocking users is a popular request. Unfortunately, network scanners aren’t able to do this. You can only block IPs at the router level, not from an individual computer running on the network. Every router has a different interface for doing this so we can’t give any specific guidance. You can ‘blacklist’ an IP so that it won’t show in the scan results, but that doesnt prevent that machine from being on the network.
Our best advice is to google ‘block device’ and ‘model name of your router’ and see what comes up. Many routers have web-based management interfaces that allow for device blocking by MAC address. It is a bit cumbersome to do on a regular basis, but it certainly possible.