How can I remove purple stains in my highlighted hair?

Have you tried washing it several times in a row?

If your hair is dry you might want to take it easy on the dye and give it some time to recuperate. Maybe try a protein treatment and a deep conditioner before you put any other harsh chemicals on it. Toners don’t tend to hold as well as other coloring agents, you might just need to wait for it to wash out, as suggested above.

I had same problem..solution for me was to dye it darker, wait a month them get professional to streak it .
I think it had something to do with Henna dye? not sure. it was ahilw ago (3years).

See a licensed hair colorist for a color correction.

I agree that you over processed your hair so that is why it turned white.
Condition for next few washes . It might take about a month to get to the point of repairing the tone. If you process it again you may lose the hair.