Depending on what amount of tomatoes you have there are two approaches : for larger amout that have been fermented in a crock for example, you can drain part of the brine and pur in equal amount of wate. That will dillute the solution but you will need to wait a couple of days before,and rotate the brine several times to give a chance to the salt that is already in the tomato flesh to exit. Keep in mind that changes in the brine solution's concentration affect the way the already fermented product will keep from that point on. Forsmaller batches that will be eaten within a 10 day period, you can simply take out the desired amount of tomatoes in a dish with a lid, and add clean cold tap water. Place in the fridge and let them sit for several hours or overnight. If they are very salty, you can replace the water with clean one at some point (overdoing it will leave the tomatoes bland though). Hope this helps some.