How to set grafana dashboard on k8ssandra ?

[counter2015]

I have deploy a cluster by k8ssandra, forward 9103/promethus port, it gives me these output

collectd_df_df_complex{df="var-lib-cassandra",type="free",instance="10.0.43.92",cluster="mycluster",dc="dc2",rack="default"} 820239441920 1656319089989
collectd_df_df_complex{df="var-lib-cassandra",type="reserved",instance="10.0.43.92",cluster="mycluste",dc="dc2",rack="default"} 16777216 1656319089989
collectd_df_df_complex{df="var-lib-cassandra",type="used",instance="10.0.43.92",cluster="mycluste",dc="dc2",rack="default"} 164550623232 1656319089989

I found a repo with grafana dashboard here
https://github.com/datastax/metric-collector-for-apache-cassandra/blob/master/dashboards/grafana/generated-dashboards/overview.json

Suppose I want to know the request throughputs.

I found the query statements in dashboard is like

(sum(collectd_df_df_complex{instance="", df="root", type="used"}) 
/ sum(collectd_df_df_complex{instance="", df="root"})) * 100

I cant found any df equals root in metrics page

Is there any step I missed to setup the metrics collect ?