The Swiss international was expelled by his team after using Twitter to insult the South Korean fans who jeered him at London 2012.
"I still have to write a letter on the website of the Swiss team to explain to people what happened," he told Radio Radio.
"I admit that I made a mistake in responding to the insults I received. I got it wrong and I admit that.
"I now return to Palermo with a positive frame of mind. I left two years ago and had the chance to play regularly while on loan at Novara, so now I'm happy to be back in Sicily. I hope to prove my qualities.
"I need to do some fitness work, but I will try to be ready for the opening game. I hope Palermo can have a good season, as it'd be a dream to reach the Europa or Champions League."