My oscar fish was fed wayyy to much , he swoll up and we thought he would die , but he made it through the ***?

he made it all night , the swelling went down , and he looks rough , idk if he will make it , hes eyesm are clouded over and bruised , i feel horrible he was a cool fish , what can i do to make it better , ? hes not moving a whole lot , and the cichid like emploded , on th inside , we put him out of his misory , but oscar is a trooper now , hes hangin on , and idk what i can do , or dont do , help me plz lol , my son is freaking out , he thinks hes dead , but hes2 so he doesnt understand that he killed the fish ,