With a lot of W-O-R-K and T-I-M-E. Not to mention TOOLS. You will need some GOOD*, SMALL, FINE triangular files for starters. BUT, BEFORE YOU DO EVEN THAT, CLEAN ALL THAT DAMNED RUST AND CRAP OFF!!! The rust and dirt were what caused the INITIAL difficulty, combined with your ham-fisted attempt at re-attaching the steering wheel. PATIENCE is NOT OPTIONAL when you work on machinery!!! Learn this lesson this time, and you won't come to such grief again.
Yes, I'd say the appearances there are quite damning. Ah, live and learn. We all must start with a Lesson like this one. I did, in the Long Ago. Patience!
The kind of file you MUST USE WILL be small enough. You don't have them yet, but if you mean to do this job yourself, you will have to acquire them. when I made my ^ above about GOOD TOOLS, I mean NO DAMNED SPOTTY ASIAN PIG-IRON!!! Great swaths of east and south Asia abound in sulphur, which contaminates their coal, and even their iron, directly. Add to this physical fact, the cultural phenomena of the Suk/bazaar mentality, especially in the south, then an aversion to forging good steel which was expressly FORBIDDEN BY THE HAN DYNASTY AFTER THE WARRING STATES PERIOD, 2500 yrs ago, and you get civilizations which DON'T LIKE TO MAKE GOOD HARD STEEL, AND SELDOM CAN ANYWAY!
So, buy your files from a reputable vendor who sells GOOD NORTH AMERICAN OR EUROPEAN STEEL TOOLS, and nothing less.
You then must use one or several of those tiny triangular files to clear the burrs and rust out of the splines on both shaft and steering wheel. Again, do so only AFTER you CLEAN THEM UP with wire brushes, and a bit of fine emery cloth. Only then may you commence filing, when you have cleared all the rust and dirt off.
Mind you, you really mangled those parts pretty badly. IFF you have the $$, then save these as a Reminder to yourself of how "haste makes waste," then, start shopping for replacements. Looking at the steering shaft, I fear that it's almost, but not quite irremediable. The steering wheel itself is a little better, but only because you didn't have opportunity to abuse it so badly.
What is your Time worth?