Easiest Countries for this is Portugal and Castile since they are closest to America and Africa. First you need to fully colonize or conquer 5+ provinces within same colony area. These will form colony nations under your motherland. Repeat three times and when that is done you open up your menu system (ie click on the country shield in upper left corner) select the subjects tab where your colony nations and any vassal and Personal Union countries are listed. Select each of your colony nation and choose reselect governor and you will replace the current governor with a 4/2/2 or 2/4/2 or 2/2/4 governor so you might improve or worsen the colony nation while doing this. You can be tactical and wait to a period when 3 colonies has crappy rulers or just do it just to get the achievement.