How does eliezer save his father from the selection at gleiwitz?

Eliezer saves his father from the selection at Gleiwitz by quickly switching places with him during the chaotic process. Eliezer's father was deemed too weak to continue, so Eliezer took his father's place in line, knowing that his father's survival was crucial. This act of selflessness and sacrifice ultimately saved his father from being sent to the gas chambers.