Signed for £27million from Wolfsburg in January, Dzeko's first months in English football were largely unimpressive.
"I was sick of it, all about this transfer. For my head, it was a little bit difficult.
"But I've had a pre-season with the team now, which I think is the most important thing for every player.
"I think I'm working hard and well, so we'll see. But I know this season will be much better," the 25-year-old told the Daily Mail.