I’m sure there are plenty of red-blooded male Americans that would love to help with this problem.
The US fertility rate is 1.87, well below the replacement rate of 2.1. The South Korean fertility rate is 1.27.
Life expectancy at birth in the US is 80.1 years (2018 est.). For South Korea it is 82.5 years. Females in South Korea live more than three years longer than US females.