You may either take a trian or a flight from Beijing to Dandong. Usually, taking a train is lower but cheaper than taking a plane.
The train and flight schedule and ticket price can be seen through Beijing trains(https://www.travelchinaguide.com/china-trains/beijing-schedule.htm) and Beijing flights(https://www.travelchinaguide.com/china-flights/cheap-beijing-flights.htm). You may take a train from Dandong to Dalian, adn then take a ship to Yantai.