Clear all old data from Zabbix in the front-end

I want to clear my Grafana instance from old test data. How can I clear all data (problems and events from Zabbix) in the front-end? But that dashboards and the panels are unchanged.

I cleared all data in Zabbix, then I cleared all browser data (session and storage). But than I get still old events and problems in Grafana.

I have looked in the database of Grafana, but I can’t see any table where data from Zabbix is stored. (I have changed the default sqlite database to a mysql database, to be consistent whit Zabbix database). But I don’t see where data is stored elsewhere.

I use grafana-sever version 6.0.0, alewanderzobnin-zabbix-app version 3.10.4 and zabbix server version 4.0.13

Has anyone done this or can anyone help?