Unfortunately, I don't have an answer for that one. There are some like Nannochloropsis that grow in both salt water and fresh water, but not knowing what you have, that is impossible to say.
I would suggest first, taking a sterilized container and add one half full of your green water. Then add some already mixed salt water (1.026-1.030) equal to about 1/3 of the volume of green water, to that green water, add a little liquid fertilizer, put under a light (I use spot lights in clamp on light fixtures), and aerate.
If the culture doesn't crash, add another similar amount of salt water and pray.
If the culture grows, keep adding salt water, until the specific gravity reaches 1.019-1.020. Put in a larger container as it grows and as you increase the salt water added, also add a very little more fertilizer.
If you reach that 1.019 s.g., and if it is still growing, just add salt water already at 1.019 about every two days. When you have as large a container going as you want to use, split the culture in two, top up with salt water 1.019, add more fertilizer, and keep it going.
If that doesn't work, try to find a supplier of LIVE nannochloropsis, buy the smallest amount they sell, and use that to start your culture.
Once you have the phyto under control with at least two and preferably more containers growing it, you can start your brine culture now and use the green water for feeding them.