Picture 1 - Once the pot is filled with soil you can remove the center container
Picture 2 - Moist the soil if it's dry
Picture 3 - Take the plant you need to transplant (ref guide part 1) be careful not to tilt the plant once it's in your hand, it could cause the soil to separate braking the root system as well.
Picture 4 - Quickly turn to plant in the holes ready to accept it, again be careful not to break any roots if possible. The less root are damage the less the plant will be in shock. Add some more soil if needed

I usually water the containers until I have a run off with plain water, no nutriments, with a Ph around 6.5, after I leave the plant in the dark for 12 hours to minimize the shock from the transplant. Past this 12 hours if dark, I keep them on 18/6 or 24/0. Wait until the soil is really dry to water again, this will encourage the roots to go deeper in the soil trying to reach for water.

If you have suggestions, comments, etc. let me know.
Hope this may help some of you !