just spin the bar like a roulette wheel!
results will be similar -98% crash, 2% jackpot!
just complete the turn,
stabilize your stance
switch feet (optional),
flatten board +/or bear off +/or sheet out as needed,
slowly rotate bar hand over hand.
It wont hurt you to ride for a few seconds with a twist in the lines, it's better to make sure you are up to speed and have the board stable first anyway, no need to play wheel of fortune.
As you get more comfortable, you can do it faster or mid-turn,
but it really doesn't matter,
the smooth power through a carve is what makes a downloop cool.
It might seem less intimidating to tackle downloop transitions with a stopper, but really it makes it harder, because you end up trying to do it all at once, rather than sequencing properly. I got much more comfortable downlooping when I learned to do it without a stopper, but to each his own.