The only way I can think of in challenging the plea is if his attorney provided affirmative misadvice, particularly about his possibly being deported. I believe there is a recent supreme court case that says failure to advise about deportation accurately is ineffective assistance of counsel meaning the plea can be withdrawn and the sentence set aside.
Your friend needs to consult with an immigration attorney and/or a criminal defense or appellate attorney to write a Rule 3.850 motion challenging his plea due to ineffective assistance of counsel based on his current immigration status, provided no one warned him this could result. I doubt he will be able to write one himself under the circumstances. Good luck.
He needs to consult with criminal attorney for the reasons my colleague states above. There are numerous ways to set aside a plea, but there are some time limitations. If his attorney provided misadvice regarding immigration consequences or if the judge improperly advised him, he may have an out. BUT...he must also show that he would not have reasonably accepted the plea but for the immigration consequences.