Go see that video on youtube
alltatup or just google "using STS to make female seeds"
Simply put :
You have plants A and B
Plant A is your chosen Trainwreck FEMALE clone or seed
Plant B is your Barneys Farm LSD FEMALE seed
You spray STS on a branch of plant A and it will crate bananas (it does have a method to do it,you don't just drown the plant/s in STS)
You take the pollen from that plant (A) and either store it for later use or use it on a plant(B) that is getting ready for pollination (20th-32dn day of flower)
Since both plants are assuming stable and female,the offspring will carry likely XX-XX genes and sprout females only!
It's quite easy if timeframes are kept tight..Not that i've done it,but leaving out the result factor of success,it seems quite easy!
Now if the seeds you started with are F1(stable hybrids from natures already existing breeds) they are likely to produce beautiful F2 Female seeds.
If they are F2 or a mix of F1+F2 you will most likely get F3 seeds which tend to be unstable and require you to recursively repeat the crossing with each parent (A+offspring=Ao | B+offspring=Bo) and then ofc if you like Offspring+Ao | Offspring+Bo and you continue to backcross and repeat the process until you have the phenotype you want! I would stop at F3 unstable seeds as it would cover my personal pleasure of breeding a few mixes....
Anything further requires good lab tests for phenotype %,THC,Genes Cannabinoids etc...