My hair has been every colour of the rainbow the past 15 years and has been almost completely burnt off more times than I can count. I have managed to turn it around every time and have it feel soft and healthy again in just a few weeks with this regimen:
Alternate olaplex 3 and oil treatment weekly (jamaican black castor with coconut oil is great for hair growth). Leave both treatments on over night with a shower cap/stretch foil.
Shampoo, mask and conditioner in the morning. Leave the mask in as long as possible too, at least 20 min.
Always use lukewarm or cold water on your hair, not hot.
Use a tangle teezer or something similar to detangle your hair without pulling it out.
Leave in conditioner after towel drying. Avoid heat styling (including hair dryer) as much as possible and air dry.
Avoid washing your hair as long as possible. Use dry shampoo in between and boar bristle bush to redistribute the oils from your scalp to your ends.
It doesnt work for everyone but trying switching to no shampoo method or cleansing conditioner if you want to be extreme. If your hair is super dry and doesnt get oily at all like mine it works wonders. You have to do a normal shampoo after opaplex or oil but my midweek washes are all with conditioner (co-wash)
Trim the burnt ends and if there any completely fried to the root bits that are unrescuable cut them off ONLY if it will not be noticable. I have crazy thick hair so if I cut off some parts from in between my layers you can’t see it all, obviously you can’t do this with short hair. If you are not 100% about this, don’t do it or have a proffessional do it, its only a last resort and I only do it because my hair has been fried so many times that I know exactly what parts will never get better and only keep making my hairbrush get stuck on them and pull out the healthy hairs around them.
Stop bleaching if you can. If you absolutely have to bleach, use a bleach bath to do it gradually. Im on my mobile so I can’t explain a bleach bath right now but it is easy to google. Basically you mix bleach with conditioner and put it on over coconut oil mask to diminish both its bleaching and harmful effects greatly and protect your hair. Doing this a few times to gradually get the shade you want is a lot less damaging than bleaching it all at once.
To give you an exampel, exactly a month ago I bleached my hair white for the 4th time this year, dyed it pink then 2 days later bleached it again, dyed it red then a week later put henna on in it and then bleached the roots and dyed it copper. Half my hair fell out from the roots. Touching it felt like touching sandpaper and there were these dried bits that stuck together that I couldnt even put my fingers through after drowning them in oil/conditioners.
Now a month later after doing the above my hair feels super soft and the awful bits are completely gone (only cut off a few at my neck because I never put my hair up). Its still falling out a lot but a lot less, especially if I am gentle with washing, drying, combing etc. I will probably be an idiot in the future and burn it all off again at one point (I am addicted I think) to get a crazy colour for a week. And it might catch up to me at one point but so far especially the olaplex/oil combo has worked every time for many years.
Sorry for the wall of text and if there is any crap spelling. I hate typing on mobile. I really hope some of this helps you, I know how awful it feels to have your hair burn off but don’t give up hope you can get it back! Just don’t be like me and burn it off again like me once you do 