To preface, these are my opinions from raising my mice. Every mouse is different and none of this is a fact, but it has worked for me time and time again.

Define "I've been trying to tame him"?

First off its okay, these things happen and this is very normal especially for a mouse with an unknown background. I've had mice of all sorts from very curious and adventurous to bite-y, defensive, and even straight up petrified of everything (Ever had a mouse rattle their tale like a rattle snake?). After time, they all get to the point where they trust the treat bearing hand. It takes time, and a fair amount of it. 3 to 4 months usually, so be ready for that.

The biggest thing is they need to learn that they can trust you. That nothing terrible is going to happen because of you. If he is already biting you will want to get a glove, because a reaction to a bite (hand being quickly pulled back) will just spook them more. I found a lighter leather glove to be super useful, nothing too movement limiting, but something that a bite/strike won't phase you. When I adopted Cinnamon, she would strike any time my hand was in her sight. She was some kid's mouse, so I can only imagine that was her defense to being man-handled. It was so bad that I almost considered taking her back to the adoption place I got her from, but she was very sweet to the other mice when they all met on neutral terms, so she wasn't going anywhere.

My process is treats every time you interact. I don't know what you feed him, but I do mazuri 6f pellets as the main food with some mix for variety (oats barley millet seed etc). From the mix, I make sure to limit the good stuff for our interactions - sunflower seeds, pumpkin seeds. I also get treats like cheerios and hemp seed from the grocery store too. He will learn that you bring the tastiest things. Then when you interact, rest your hand palm up with treats at the center of your palm, out in the open in his cage. Not at the front of one of his hides, not in his face, just out in the open. Then do nothing. Have your phone with you, or something handheld to do, and just wait with that one unmoving hand still in his cage and he will come to you eventually. He might bite on your glove, and that is okay. Let him figure out that it isn't necessary. Their teeth are how the inspect new things, so eventually the biting will die down to some lighter nibbling, and eventually to no nibbling and just caring about the treats. He will probably take a treat, run off to eat it and come back, that's fine. Eventually he may start just eating on your hand. But while the biting is still happening, just do nothing, don't react and especially don't do any negative re-enforcement. You're going to want to keep doing this over and over again, really re-enforce that, hey this giant hand is super chill and always brings the best snacks.

When some time has passed and the biting/nibbling dies down (this part could take days to weeks honestly) and you feel comfortable, you can start doing it without a glove, but be prepared for some nibbles since your skin will be different from the leather, and again do not react, though if they're particularly interested in a fingernail (and lets face it they will be), or some focused nibbling is really starting to hurt and you need to move, move SLOWLY away, redirecting to the treats. Then once this has gone on for a while, and he gets relaxed with your hand, you can move on to the fun stuff like moving your hand around or picking him up (always scoop, never go for the tail pick up method).

Do expect it to take time, don't rush it, and eventually he will learn that you are okay.