There is a leather cleaner and conditioner pack that i have used for similar things I would recommend

https://www.amazon.com/Leather-Honey-Conditioner-Accessories-Concentrated/dp/B08632JVYG

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I've revived many a thrift store leather bag disaster with this.

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The very very slow method is using a damp paper towel, and slowly scraping then drying so the water doesn't actually soak in, but that will take a very very long time.

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good luck!