Long after the bacteria tinea versicolor was determined gone from my chest, the lightened skin patch remains. how can i restore my skin pigmentation?

Whoa: First, tinea versicolor is a fungus, not a bacterium. Second, culture is famously unreliable as a means of determining that it's gone. Third, the fungus is ubiquitous and returns quickly -- you manage tinea versicolor long-term. Fourth, a single depigmented patch is unlikely to be tinea versicolor. Perhaps there is a misunderstanding or you need a second physician's opinion.