This was covered years ago, but I can only imagine the innumerable amount of threads that came up with your search query. So luckily, I can remember a few key points about this from way back…
What you do is you kegel for a few seconds, then do an A-Stretch while reverse kegeling. The only reason I remember this, was because way back when I first began PE, that routine gave me my gains.
Now that I look more into the mechanics of the technique, this kegel/stretch/reverse kegel idea seems like PNF stretching, where you activate a muscle against the stretch, then relax it to allow stretching beyond that point.
Do a search and look for "DLD Blasters". If the thread is still around- it’s got tons of info in it.
Actually searching brings back tons of results too… just read the original thread here:
DLD Blasters…Un-Real Length Gains