I did one about two months ago. I had been using affirm no/lye and switched to affirm lye. It was done by a good friend that does most of my relaxers (unless I'm traveling and have to do it myself.)
Basically what we did was this. I had a little over 8wks of new growth. So we parted my hair into 6 sections. She applied the relaxer to the new growth only in the top two sections and the two back sections. I applied the relaxer to the two front sections because I could look in the mirror and see those sections good. Once applied, she smoothed through her 4 sections and I smoothed my two section. This took about 20 minutes. Then, we applied the relaxer all the way through to the ends of my hair and left it on for about 5 minutes, and started the rinsing process.
Since then my hair has been a lot less dry and has a lot more bounce & movement. For one while it started breaking & shedding really bad and I thought I had made a huge mistake, but for me it was the daily infusium 23 that was breaking my hair. Once I stopped using that and did some treatments, it's been improving more and more.