I have turned clients down that have box done red DIY style that have done this recently b4 coming to a pro, without letting the color fade out a bit. If its a fairly fresh box job they have done, the red pigment is super strong impossible to blonde it up like they usually request!
I have had success with a de-colonizer my fave is Solaris, you can mix it with h20 for subtle lift & up to 20V=6% developer for max lift,shampoo it out,dry hair then bleach up to 20V over de-colored hair. I have found Solaris leaves the hair in good health for a lightening after. But still results in a Lv.9+CG/GC or light strawberry.
Use a color/toner that matches the underlying pigment levels of the pink/salmon hair after your lifting processes are done,raw & dry. If using permanent color with low peroxide, let it stant 10mins after mixing to not open cuticle more than needed. Add in some Green/or greeny grey based intensifier up to 5mls/30mls formule even if target color is a 7+N/G/A to amp up the ash to cut the super stuck red/copper pigs......If hair is porous,apply toner/color to damp hair & keep an eye on it.You should charge more 4 services like this as color corrections!
& Do not be afraid to query clients thoroughly that have DIY color seeking your advise, as their most recent & number of times they have done DIY colors. I had a lady with fresh red box color snap @ me " can't you put bleach on it!" I responded, " If your fond of the color pink, sure I can" I told her to wash her hair alot,use laundry soap & leave it on 5 mins & when it starts fading,come see me.....or go darker!