You should read document of Prometheus, Grafana just interface to show graph.
If your host has some rule can follow, you can click EDIT at top or graph, try change instance=“$host” to instance=~“^db08.*”, mean any host start with db08 will show in graph, it use regular expression.
Reference: [url]https://prometheus.io/docs/prometheus/latest/querying/examples/[/url]