If I am allergic to iodine how will they clean my skin before surgery?

Allergy to iodine. There are many other preoperative antibacterial scrubs that don't contain iodine such as hibiclens, ethyl alcohol and others.
Several options. There are several options available for surgical skin prep. Many surgeons have actually moved away from iodine based preps to a combination of alcohol and chlorhexidene. Just make sure you tell your surgeon and the or nurses about your allergy.