technically, buying one of those synthesizer guitar modules that can retune your existing strings to anything, is the fastest/easiest, but, it will cost you & still not the preferred way.The fastest way is to tune down the strings you have and play really soft.
That’s not the best way, but it’s the fastest and easiest.
Or, you can do what Billy Sheehan does & have a doubleneck made just for that.
Billy Sheehan: Why not a 5er instead of a 20lb double?