I have 3 (2black 1 bare) wire 220 coming out of my kitchen. How do I convert it to 4 wire for my new stove? Or do I have to run a new line from my panel?

Why do you need to? You can use it if you want to. The range instructions should have a wiring diagram showing both ways of wiring it.

If you need or want a 4-wire feed you MUST run a new line. You cannot "convert " it.