If the hair is not installed
detangle the hair as much as possible without losing more hair and then seal the wefts with any good weft sealant i.e. fray block. Allow about 24-48 hours for the sealing to dry completely and then give the hair a good clarifying poo followed by a mild/medium protein treatment for about 5-10 minutes.
Finally, saturate the hair in silicon mix (or Nexxus Humectress - not as good but OK). Next place it in a plactic bag and microwave on medium heat for about 1-2 minutes.
Take out the hair let it cool down and rest. Rinse with cool water and voila brand new remy goddess hair.
If the hair is installed you may be limited to doing a clarifying poo, medium protein treatment and the silicon mix. You will have blinging hair but the wefts may still shed.
ETA: I know this bc I used the same batch of Remi Goddess Yaki 3x and I still ahve it and am considering reviving it again to doctor one of my old synthetic half wigs. Love this hari as you cannot go wrong for the price.
Also I just wanted to say that this hair does not like certiain shampoos, conditioners or too much product. In fact all I used on this hair to revive it was a light mist of rosewater every few days and John Freida heat protectant (water based) when I needed to revive it. This hair does not like greasy, heavy products. These sort of products will weight it down and even make it tangle up really badly. In essence you have to treat it as the original (Chinese) Type 1 donor would treat their hair - min product.