I use mostly Mehandi henna/indigo mix and have used Surya 2xs. I use Mehandi henna/indigo mixed together to create shades of brown.
I've been using henna/indigo for over a decade off and on. Several times I have opted to remove it for a change. It did not always go well. I've had orange hair and once orange with green tips. This is important, I use body art quality (BAQ) Henna/Indigo. I have used a mix most recently made by Surya but it did not have any metallic compound. If you didn't use pure BAQ or are unsure if it was a non-metallic mix than the removal is going to be much more difficult and I have on experience in moving that kind of henna/indigo.
I have tried everything from bleach to different hair removers. Bleach is a no go when indigo is involved. Due to the blue base it is more likely to go green than the usual stages of color lifting. Of course it all depends on your hair and how long you have been using henna/indigo mix. You can of course test strip to see how it will lift but I suggest avoiding bleach either way given the damage it can do to the hair and if you have been using henna/indigo your hair is probably is beautiful condition. No sense in ruining your healthy hair.
As for removers Colorfix helped remove the henna but barely touched the indigo even after 3 attempts but it did not harm my hair. When I tried Colorfix I had years of henna/indigo on my ends and that makes for difficult removal. If you don't have don't have years of dying with it than Colorfix might be your best option. I used the finishing lotion. I suggest using the lotion because it helps you know if there is still color there you do not want. Otherwise it will just show up days later.
I have found that L'Oreal Effasol Color Remover to be the best removal for henna/indigo with years of color buildup. It is gentle enough to use several times on healthy hair. I use the water method listed on the package to remove levels 7-9. Now you still follow with a 10 volume developer once you have the color lifted so make sure to read the directions on the package before using. I don't use the removal option with the developer because it can have bad effects with the indigo. I had to do the removal 3xs but it lifted enough for me to color again. My ends were black from years of using henna/indigo. Make sure to follow with a good deep condition if your ends feel dry prior to recoloring. When you recolor use Neutral Protein filler or Ion pre-color treatment to ensure even color application. Now keep in mind that using the water method and this is a removal product you won't have the lift stages like using bleach. It will lift the color and it might lighten the hair a little. Also remember this will not restore your hair to your original color. If you have very light hair level 7 or higher you probably will not be able to get back to your natural color just yet and will have to wait a while before lifting higher. I would not expect your hair go higher than a level 5-6. When recoloring pick a shade 1-2 levels lighter than what you want. I suggest using a demi color instead of a perm or semi color. Follow with Ion after color treatment for sealing in the color. If you are using henna and indigo I would use less indigo or you might go dark again.
I hope this is helpful and everything I have mentioned can be found at Sally's. Please monitor the condition of your hair as you lift out the henna/indigo. If you can tell your hair is getting weak stop the lifting process and do a deep condition then come back to it in a few days.