There are several ways to go.
1, there is an express train to Bama. I'm not sure exactly where to take it. You can refer to the advice upstairs or call the bus station in Guangzhou yourself.
2. Take the express train to Nanning first, and then take the express train from Nanning Peking University Bus Station to Bama. There are more buses to Nanning and Bama, which is very convenient. You can also have a rest in Nanning to avoid long-distance fatigue.
3. Take the train from Guangzhou Railway Station to Nanning, and then take the express train from Nanning Peking University Bus Station to Bama.
4. Guangzhou flies to Nanning, and then takes the express train from Nanning Peking University Bus Station to Bama. You can often buy discounted air tickets. I bought a discounted ticket to Guangzhou before I went to 240 yuan. It was a good deal and saved a lot of time. I suggest you fly. Good luck.