If I can fix immigrant status, how and where do I start?

Your question requires an attorney consultation. It is not a simple question that can be answered on this type of forum. There are many factors that would need to be considered and evaluated. Why was your husband deported? Does he have a criminal history?

You need to determine why he was deported, what statutory bar applies to him, whether he has any criminal history (and if so, what exactly he has in terms of arrests and convictions), and from there, you should be able to determine what avenue may be available to your husband. I recommend gathering up all his documents, including the removal order and any criminal convictions and consulting with a U.S. immigration lawyer as to your options.

Your first option is to file a Form I-130 petition for your husband with CIS office closest to where you reside in Mexico. Whether your husband can in fact return to the US depends amongst other things the underlying reason(s) for his deportation. Some deportation grounds such as unlawful presence or visa overstay can and in fact will be waived. Some other grounds of deportation such as false US claim or certain criminal convictions cannot be waived. You will need to consult in depth with an experienced immigration attorney to determine the actual basis for your husband's deportation