No rule for this one
No ending or word group predicts the article of Konzert. Learn it as a pair and say it out loud: das Konzert.
das Konzert
It's das Konzert. Konzert is neuter, plural die Konzerte.
Das Konzert war gut.
The concert was good.
No ending or word group predicts the article of Konzert. Learn it as a pair and say it out loud: das Konzert.