What is truth about color removers?

[Ccddmm]

so my sister is in cosmetology school and soon I will be too... I want her to use a color remover... she asked me to do so research... but I’m not really getting the inforamation I need...so my hair was platinum blonde for many years ... and like a dumb ass I died it blue black semi permanent and then red black permanent... the red black hair dye has this color locking agent... which I read can be tricky with some hair color removers...I really don’t want to bleach my hair first I would like to lighten it... and anyone help me get to the truth about hair color removers...