The NagVis map config files can be found in /omd/sites/[sitename]/etc/nagvis/maps
In https://[servername]/[sitename]/nagvis/docs/en_US/map_config_format_description.html you can find the docs.
Probably you need to find specific hostgroup definition and remove it.
define hostgroup {
hostgroup_name=servers
x=100
y=200
}
I believe I was able to edit the config files without stopping / starting the site in the past. Just don’t try to edit it with both gui as cfg at the same time.