H2s odor still lingering

I have a large batch of blackberry (18 gallons) that I started in early
April of this year which developed H2s in the primary, I splashed
transferred and treated with Bocksin but several months later I can
still notice a slight H2s odor?
Does anyone have a cure for this residual odor, I thought I read
somewhere in the past that treating with Potassium Sorbate may help but
can't remember any details.

Rick

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