Time and lots and lots of patience.
I have a glider that came to me from a rescue. I believe someone had teased her with treats. Every time I offered her a treat she would frantically grab at it with both hands and at the same time lunge to try and get it with her teeth. The result of her efforts usually either knocked it out of my finger tips or she would miss the treat and bite my finger enough to bleed. It took a long time for her to understand that if I offered her a treat it was hers to enjoy.
Try using a popsicle stick for treats your glider can lick off like yogurt, honey or baby food fruit. This will protect your fingers. You can also use one of those tiny spoons that ice cream stores use for samples (Baskin Robins has cute little pink ones). The little spoons will hold a piece of fruit or even a yogie to offer your glider.
As your glider gets used to your hands bringing yummy things, you can gradually move your fingers closer to the end of the stick or little spoon and eventually just offer treats with your hands. It took Dot about 6 months to learn to take a treat from my fingers gently. She would get excited now and then and still miss and end up biting my finger but it never seemed like she was biting just to be biting only if she thought the treat might disappear before she got it.
Just take things slowly with her. Sudden movements might frighten her. Try to stay calm around her too. Gliders sense when we are tense or afraid and react to our emotions too.