gjcore. You can try to train them going down but it's not the way they want to grow. I would either let them be or find a way to add additional height to the trellis. If you let them be they will try to keep growing taller but find no support until they grab onto something lower making a somewhat thick mass.

How do you keep pole beans from growing too tall?

Prior to pruning or pinching the pole beans at the end of the growing season (late fall), make sure it has set pods and then use sharp scissors or shears to cut the main stem back to the desired height. Do not cut lower than set pods and cut back any of the pole bean that is taller than its support.

Should pole beans be topped?

Pinch off the tops of pole bean vines when they reach the top of the support. This will force them to put energy into producing more pods instead. In high heat, use row covers over young plants; hot weather can cause blossoms to drop from plants, reducing harvest.