How exactly could I set the history metrics so that it would show data only for the past 72h?
I've modified the history value in 259,200 Seconds in /opt/netdata/netdata-configs/netdata.conf
and also copied netdata.conf in /etc, but it's showing me the data for the past 5 days not 3 now.
If I understand correctly, you are asking for some netdata configuration. I will leave it open anyway in case some of our forum users can help. But maybe it's better suited in their forum.