Broken terrain after changing resolution and nonability to go back

Hi! I created unity terrain everything was fine then I started to colour it and I changed resolution and it broke my shapes of terrain. Im trying to fit proper resolution and while it had to change it permamently on the lower When Im importing previous versions od scene I have all the time the same problem even at the beginning I rechanged quickly resolution on the highest (after noticed the problem), but it dont fix that. Everything is staying right there like in the low resolution even I can now sculpt in the higher once again but I dont want because is a lot of terrain. I want only back it from the previous scenes terreain with old details :?