Ok I confused "bending" with "tucking"
From the link to the guide I copied a quote that describes my confusion. Here it is:
"During the vegetative phase, make sure to bend any parts that are poking their way upwards back down, so they remain on the same plane as the other parts of the plants. This will allow all the plants to grow upwards in even rows, maximizing the energy from the grow lights"
Now I understand what was written except for when to release the part that was bent, when do you do that? It doesn't say...