How do I redye black pants that have bleach spots?

What is the fabric content?

Use Rit dye. You can find it in the laundry isle of most grocery stores or at the craft store.

I have done that in the past, dropped bleach on material. I took a sharpie pen and colored the spot and rubbed it in with my finger to blend it better. You cannot notice it at all, but it might depend on where the spot originated. Hope this helps

Try in a tiny spot either sharpie magic marker or a black laundry / fabric marker , they are both permanent . If you just re dye them black, the areas that were bleached might still show up lighter . You might want to try the marker way first , then dye them afterwards .

Get a black laundry marker by Sharpie, it's more permanent than the plain black marker. Then just color in the bleached spots, let dry thoroughly, then launder them.

Conventional dye such as Rit will only work successfully on 100% cotton.

The results on fabric having any, or partial synthetic content, such as polyester, will be blotchy and inconsistent.

A quick way to determine if fabric has any synthetic content in the fibres is to scrunch up in your palms, making a tight ball, then release. If it 'bounces' back to what it looked like originally, and smooths out easily, it likely has polyester.