Used Sweetened yoghurt in savoury dish - how to correct?
You cannot disguise or remove the sweetness, once it is in there it isn't going to go away. You can balance it out with acidity, however if it is very sweet then you will need to add a lot of acid, and then the dish will be intensely sweet and sour, which probably is not what you want. 

You aren't going to be able to regain the character of the dish, but you might be able to produce something tasty. I would try to add some bitterness, like fenugreek if you have it, and see if that makes it work. There is a point of diminishing returns where you can spend more time and effort adding more and more ingredients to rescue a dish than it's worth, at that point it's better to start over or feed it to people and tell them it's your grandmother's recipe - nobody will ever tell you it's bad then.