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piece of cake dude you need a scotch pad they are a bit like a Brillo pad you could try a bit of wire wool and re brush by rubbing it the same way as the grain , do a test piece underneath where you can't see it to see what you think this will do the job mate
Can be tricky freehand, I've seen it done by cutting a slot in thin, hard plastic and using that as a guide to keep the "grain" as straight as possible.