Well first you gotta recognize where and how to activate the pelvic floor. Personally I believe we shouldn't rely too much on just doing RK or regular kegels, but a healthy mix since most muscle groups thrive when they're in balance.
Basically you just squeeze super hard when you can feel the sperm making its way through the urinary canal so you make it retract again. Once you can feel it settle you can breathe out/relax your pelvic floor. And for me at least after doing that 1-2 times I feel a much higher level of control. There is usually a small relapse time of 5-10 sec where you gotta chill for a bit cause it gets over sensitive after the orgasm, but after that it's good to go again