You shall first check the sunglasses and find what are problem of your sunglasses. And usually, the most common damaged areas are screws, hinges and bridge of the nose. Find the damages part, then use small screwdriver to tight your screws if it is loosen. If you want to replace damaged part of your sunglasses, you shall first find substitutes. Then lose the screws, and then take the damaged part out and put on the substitutes. Next, tight the screws. If you still have no idea how to deal with it, you can have an optician to do it.
Vintage style is also my style. I love this, and I collect everything vintage which includes clothes, small ornaments and so on. As for vintage sunglasses, I have several pairs and I once did the reparing thing myself. First of all, you need to make sure what is wrong with your sunglasses by examing yours very carefully. If it is about the nose bridge, I can assure you that it is no big deal. And just screwdriver can handle this. It is too hard to teach you here, just by some words, so I think you had better find some useful videos online to make this achieved.