How can I fix receding gums with braces? (Photo)

Hello, I have been wearing braces for like 3-4 years already and I'm starting to worry about my lower teeth specially because I noticed gum recession (please refer to the pictures I provided). So my question is how can I fix this problem? I am also very troubled because of "black triangle" I have. I don't feel any pain when brushing and eating. I took these pictures by myself with my phone so I apologize in advance for the blurry ones. Kind regards.