I was able to confirm with Simone Hofmann (production of Metrobeat contest 1993-1996) that Rammstein played in February 1994 for the contest.
This would mean that it would be one of the first concerts with the unfinished formation, as it is known that the first concert with the 6 members was in Leipzig on April 14.
"...Rammstein was a part from the Berlin Music Contest
(Pool) „Metrobeat“ 1993/ 1994. Sorry, I can´t remember the exact date.
The event took place in February 1994 in the „Kulturbrauerei Berlin,
Kesselhaus & Kantine“..."
"...Metrobeat took place only on two days. Each band played only once either Fridayor Saturday. Yes, it is also possible that bands performed under
a different name...."