Old and dark tattoos are truly difficult to fix. I'm sure the specialists at https://thefalltattooing.com/pages/tattoo-cover-up, who specialize in cover-ups, will help you. I never regretted turning to them for a difficult job. They evaluate the density of the old pigment and create a new design that can completely cover the old outline. I had a dark tattoo on my forearm covered by them, and now the old ink doesn't show through at all. I'm very pleased with the work my artist did.