Removing lowlights on blonde hair?

Hi everyone. I’m new and I don’t have a crazy color story or anything, but I need some advice.

I have naturally blonde hair, I guess between a dirty/gold blonde. About 6 months ago I got lowlights in it (I had it done twice because the first time you couldn’t tell anything was different). Recently I’ve been wanting to go back to my original blonde color, so I told the girl who did the lowlights and she explained that she would do a bleach bath.

I was expecting the bleach bath to remove all the brown streaks of dye from lowlighting, but it only made everything lighter. The blonde part looks great and I’m happy with it, but the brown streaks are just like a reddish lighter brown now. What I was wondering is, is there a way to remove them? Should I ask if she can do another bleach bath, and maybe just focus on that part?

Another thing I’ve read about is Vitamin C, and I was thinking I would try this just on the lowlighted part, just to see if it made a difference. I only have Vitamin C powder but I think that would work the same, right? Mine is ascorbic acid, if that means anything. I don’t know whether or not it matters. Everyone just says to use the tablets. I’m also not sure if this would have any affect considering the streaks are 6 months old, maybe that’s why the bleach bath only lightened instead of removing them.

Anyway, that’s it. Thank you for reading!