How to view the first/last entry in the database?

Hello everybody!
I have no experience in influxdb and I’m sorry for my English…
Prometheus remote_write and remote_read configure to InfluxDB 1.6.3.
In influxdb.conf file, the max-series-per-database parameter is set to 1 million.
The limit is exceeded and records are dropped. It is logical to assume that the old (first) records are dropped and new records are written? New metrics may not be saved, because after restart of Prometheus (OpenShift) dashboard of Grafana does not show the recorded metrics (data source = Prometheus). How to check it?
I need to understand which time range of metrics fits into this limit or which record is the oldest (first) and newest (last) at the time of the request? What SELECT should I write?