Take it back.
No matter how smart the dog, I have found that the most effective way to correct behavior issues is to keep it as simple and consistent as possible. A very firm "NO" while making eye contact with the dog is amazing--as long as you say it while catching Dog "in the act," and maintain that eye contact until the dog looks away. That's dogese for "you win." I know this sounds like ridiculous advice, but over the years I've owned and fostered a variety of rescues, all with some behavioral problems, and the simplest and most consistent route has always proven effective.
Incidentally, my parents had an ESS with severe epilepsy. I wonder if that's a commn ailment in the breed. Crash had to be put down fairly young, just past seven, due to liver failure (drug related). Best of luck with yours!
Both Springers and Cockers have problems with epilepsy. I did not know this before getting the Springer. I knew that they can have problems with hips and eyes (as many breeds do), but I never saw anything about epilepsy when reading about Springers before we got her. Show-bred Springers also have problems with a Springer Rage Syndrome that seems to stem from one male, but it doesn't show up in the Field-bred ESSs.