I used to have eczema all over my butt cheek and now it turned into a dark tone scar, will it ever fade or it's going to be permanent?

Likely fade: Most often, after eczema or inflammation in the skin there is some change in the pigmentation. For some, it is lighter (hypopigmentation); for others darker (hyperpigmentation). This almost always fades in time, though it can last a for several months in some. Generally, good moisturizing and strict sun avoidance are helpful. In some cases, prescription bleaching creams can speed this up.