@splunk_kk, try the following based on Splunk's Licence Monitoring Query
[ `set_local_host`] source=*license_usage.log* type="RolloverSummary" earliest=-30d@d
| bin _time span=1h
| stats latest(b) AS b by slave, pool, _time
| eval Date="Date:".strftime(_time,"%Y/%m/%d")
| eval Time=strftime(_time,"%H").":00"
| chart sum(b) AS "volume" by Time Date fixedrange=false limit=31 useother=f
| fields - _timediff
| foreach "Date:*"
[ eval <<FIELD>>=round('<<FIELD>>'/1024/1024/1024, 3)]
| rename "Date:*" as "*"
PS: The macro set_local_host is defined in Search App hence in order to use this outside of Search App you would need to use the underlying query instead or make the macro global.... ie. use the following instead of [set_local_host]