I think you should go to visit the Great Wall in Beijing (https://www.travelchinaguide.com/china_great_wall/scene/beijing/)

At Zibo Railway Station, there are 5 high-speed trains departing to Beijing everyday, taking about 4 hours on the way. However, since these trains will arrive at Beijing in the afternoon,you have to stay one night in downtown Beijing and then visit the Great Wall by bus the next day.

The train schedule between Zibo and Beijing could be search on this page: https://www.travelchinaguide.com/china-trains/