Based on the help of the Vehicle Body 3DOF Three Axles, front hitch forces and moments are listed under "Input signals"; however, I don't see these two inputs in the block.
I'm wondering how I add more hitch to the model? Thank you.
The "Hitch force" input port is indeed there in the Vehicle Body 3DOF Three Axles. If it does not show up for you by default, you can double click on the block and go to the "Inputs" section and enable it as shown in the image below: