p0303 misfire on #3 cylinder and this is the only code. what is the fix?

Bad coil , ,wire ,plug ,injector. You need more testing..

Most often on my escape was a bad coil. Each spark plug has it's own ignition coil on the plug which is just 1 small bolt and electrical connection. Fronts easy to get to on V-6, rear 3 are very labor-intensive. If 4 cylinder, then should be no big deal. Could be bad spark plug too.