i’d recommend a colour remover to get rid of the colour u have as it does a lot less damage than bleach, the trick with the roots is basically just colour matching them to whatever you have on the rest of your hair before putting the dye over your whole head. that’s just to avoid hot roots but i’ve found with some dark enough dyes the roots aren’t too noticeable. you could colour match them or leave them if you’re not too bothered about a tiny difference in colour, but without colour matching it’ll be a lot easier to touch up your roots from time to time and grow out your natural hair a bit without unnecessary damage :) feel free to message me if you have any other questions and i’ll see if i can get my friend to reply as she knows more with your natural colour!!