How can I treat skin pigmentation on my lower legs?

I will have to agree with Dr Irenaeus that it is difficult to diagnose a pigmentary condition without an examination and assessment.

Eczema is an inflammatory condition and often leaves a mark even after resolution. These marks are called Post-Inflammatory Hyperpigmentation aka PIH.

This can be treated by:

1. Controlling your eczema (moisturizers, topical steroid creams etc)
2. Lightening creams
3. Q-Switch lasers

Nonetheless, the first step would be to seek a professional medical opinion.

Hope this helps. All the best!