There's nothing too mysterious about the process. You have one basic objective which is to spread the dropouts equally on both sides so the wheel remains centered in the frame (assumes it started out centered).

I'm not a fan at all of the turnbuckle method for a number of reasons. The main one is based on the physics of bending steel. Bending steel involves increasing stress to flex it until it reaches the yield point at which it will bend. You can demonstrate this principle with the spring from a cheap ballpoint pen. Pull it apart a bit and it springs back to the original length, but if you go too far it'll deform and it'll spring back to a longer length.

Applying this to your bike and you'll you'll understand why I don't like the turnbuckle method. As you tighten the turnbuckle the frame will spring open fairly symmetrically because the chainstays are of similar strength. But once one side reaches it's yield point and begins to actually deform no more tension can be added so the second will never bend, and all the permanent distortion will be to one side, spoiling the symmetry.

So you need to bend from one side at a time, carefully checking that you're only going half way. I use a method similar to what SB proposes. I make a gauge the width of the dropouts from an axle, or scrap of anything stiff I can cut to length. Then I bend one stay being careful to know which. You can use a 2x4 if you like or do as I do and lay the bike flat, and stand on one stay about half way to the BB, and lifting the other holding it from the end. The one I'm holding will bend will flex feeling increasingly "heavy" until I feel it begin to move, at which I stop and check with a gauge. With practice you can judge the amount of bend you create, but I expect you'll do it by degrees until you have half the spread. Then flip the bike and repeat for the second side.

When finished you might check with the string method to see that the frame is aligned. Actually you might what to do a string test first, so if it isn't right you can align it at the same time as you spread it.

This is actually very easy in practice and, unless you're mechanically declined, you shouldn't have any problem.

BTW- I didn't look up your bike, but it has to be steel, otherwise none of the above applies.