Want to travel to North Korea and South Korea at the same time, is there any travel agency you can recommend?

If you are in Dandong, it is easy to apply for a one-day tour or a few-day tour to North Korea. Then if you travel to South Korea, you can apply in advance in Shenzhen, and then enter South Korea directly by boat from Dandong or by plane from Shenyang, but you can't enter South Korea from North Korea.