It was used to de-lice the Jews. Lice were the main spreader of Typhus which was killing many at the time. Close quarters living caused lice to spread, hence shaved heads and showers with Zyklon-B added to kill the bugs spreading disease.
The narrative about zyclone-b killing Jews is so easily debunked.

You would think people posting on this platform would know better, but are still spouting the long debunked bullshit about those nasty 'Nazi' and the fictional 6 million. I found out it was a hoax in 1998, 23 years ago and so called enlightened people still believe this shit.