I don't have much input on how to tame leopard geckos because there pretty much naturally tamed geckos but however multivitamins although not needed it is good to have. Because it contains lots of vitamins and minerals your leopard gecko might not be getting causing it to possible get a vitamin deficiency but u also want to choose the multivitamins carefully because too much vitamin A could lead to problems I recommend Herpivite by Rep Cal which doesn't have vitamin A so u wont have to worry about to much vitamin A causing problems but instead has Beta Carotene that is converted in vitamin A.
I HIGHLY recommend that you check out Leopard Gecko's channel on YouTube. She's had reptiles for 10 years and is very knowledgeable. She reads published research papers and will link to studies done if she cites them, so it's not just some opinionated person but someone who takes the time to research these animals natural habitats, etc. She's great to listen to as well https://www.youtube.com/watch?v=RsbGYBaflDc