I left Catholicism for Orthodoxy a while ago, and was received purely by confessing to an Orthodox priest and reciting the creed. I wasn’t rebaptized or confirmed. I would now like to come home, but I’m unsure as to whether it’s just a matter of going to confession, or whether something more would be required having formally entered into schism.
All that is necessary is to go to confession and explain your situation to the priest. He will give you direction on the steps to take. (So far as I know, confession is all that is absolutely necessary, but the priest may recommend a formal affirmation of the faith by recitation of the Creed.)