This method can't be used on bettas. Mainly because bettas are too small to handle. This method is more popular with bigger species that fertilizes eggs externally and without embracing. Carp, gold fish and their kinds are commonly bred that way. It's harder than it looks...... I haven't had much success with that method.
Cat fish, carp, and other types of consumption species (don't know their English names) are often bred by taking (I think) the brain cells from the male and injecting them to the female...... it's been decades ago - I forgot exactly what or how.