You use a shampoo that has sodium lauryl sulfate (the harshest), ammonium layreth sulfare (also harsh), and sodium laureth sulfate (a little gentler). There are also many ingredients out there, when they end in -fates, that is a sulfate.
I messed up my CG journey and I had to start all over again. I washed my hair with a clarifying shampoo that has both sodium lauryl sulfate and sodium laureth sulfate. It was harsh on my hair, obviously, but I had to use it to remove the silicones in my hair that I unknowingly placed in these past several days.
After that wash, I use my VO5 Moisture Milks Strawberries and Cream Conditioner. It is very cheap and CG friendly (has no silicones and no sulfates in it).