In the DMG page 255-256 are several siege weapons described which are actually objects. It takes actions to load, aim and fire the siege weapons. For the ballista for example it says:
It takes one action to load the weapon, one action to aim it, and one action to fire it.
I have always imagined you have to stand in 5 feet of the object and then take the "load", "aim" or "fire" action. In the decription for Mage Hand it says:
You can use your action to control the hand. You can use the hand to manipulate an object, open an unlocked door or container, stow or retrieve an item from an open container, or pour the contents out of a vial.
So technically the mage hand can manipulate an object but can it "load", "aim" or "fire" a ballista?