I have dry cured some chicken slices with a lot of salt. I will cook it in a soup however I do not want the salt to be released/come out of the chicken. Is it best to saturate the soup water or if I just buy say 20 grams of salt into the soup will that be enough to ensure the salt doesn't come out of the chicken?
Assuming by "dry cured" you mean you salted it and let it sit for a reasonable amount of time (hours to a day or maybe two), don't boil it. Bake it, roast it, broil it, grill it - all the seasoning you put in during curing will stay in. And assuming you don't overcook it (use a thermometer!) it will be about as tender and juicy as chicken gets. The whole point of that salting process is to make it hold up well to cooking with dry heat.
If you want it in soup, you can still chop it up and stir it into your soup when it's nearly done. Assuming you're making a plain chicken soup, you can still make a nice flavorful stock from the bones - no need to have the meat in it for that.
If you simmer or boil the chicken, you're defeating the purpose of dry curing (just like with brining). Every minute you cook it you'll be leaching more flavor (and salt) out of the chicken into the broth, so just don't cook it in liquid.
If on the other hand you essentially made chicken jerky, then you will have to rehydrate it of course - but that's not really a good way to make chicken soup (the texture will be messed up), unless you're in a situation where you need to preserve meat without refrigeration. If this is what you did, I guess the best thing to do would be to rehydrate with a minimal amount of water, just enough to cover it and let it reabsorb. Then you can add that to your soup at the end. But again, the texture will not be like that of fresh chicken, so I doubt you want to spend time making chicken jerky just to do this.
you'll need a soup base that is nearly as salty as the chicken (say %6 solution) so the salt doesn't leave the chicken and try to establish a new equilibrium between the saltiness of the chicken and soup.
This may mean that you might have to hold a portion of your soup back to add after the chicken is pulled out so it becomes less salty, but maintain the chicken flavour.