Same as for any other. Draw a line from the tip leading edge to the root trailing edge. Draw another line from the root leading edge to the tip trailing edge, making an "X". At the point the lines cross, measure 25% - 33% of the total chord back from the leading edge. This will be the proper CG.
Every plane needs a CG, or "Carl Goldberg" to fly. This point is named after the venerable designer of RC planes, Carl himself. Most kits include a "Carl" with the instructions or even printed right on the plans. If your plane doesn't have one, I have a few left over from abandoned kits. I'll be glad to sell you one. Just drop me $10 + $20 shipping and I'll send one right out.
Dr.1