So hypothetically do we have the knowledge? Yes. Orbital mechanics and the force need to apply to each object are pretty easy math to calculate once we know their mass and current orbit.

However its not a practical exercise.

The entire mass of the asteroid belt is only 3% the mass of the moon. And some 40% of that is Ceres alone with 62% being in the largest 4 asteroids. So you need a lot more mass to make anything approaching a planet. The larger the object the a harder it is for us to move.

It also takes a lot of energy to redirect masses like that, and time for the orbits to coincide and come together in a manner thats not gong to cause catastrophic break ups sending rock where we dont want it. Yes we can minimize the collision force, but that takes more energy. We dont have the technology to manipulate hundreds of thousands of rocks and get them into a single area in any kind of reasonable time scale. Hundreds of years if not longer. Its not just the shear volume its finding a way to apply enough energy to the larger objects to change their orbits significantly in a life time.