The blue you are using is rather close to the 'B' in rgb. Cmyk doesn't get any brighter blue than the 'C' in cmyk. It looks that in the cmyk version there is still al lot of magenta in the color, so you could try to remake a cmyk-version that comes close. But it will never look the same. First set a new document to cmyk, next to your rgb original, and search for colors that you find acceptable. It is always a tough discovery and you have to learn, one day, that those eye blinding colors in your rgb designs only work on monitors. So you should avoid them if the final result will be printed. There are advanced techniques, printing in six colors, that can mimic the rgb gamut, but those are very expensive. Good luck!