Look up raptor rescue and protection groups in your area and globally on the Internet or at your local library. Most states with native raptor populations will have a raptor rescue group, and some of these groups will run training programs for volunteer handlers.
Enter a conservation degree course at the university of your choice. Many of these programs require or offer internships with conservation groups or nature conservancy groups, which may offer raptor handler training as part of their educational service.
Call local- or state-funded conservation groups, whether they work with raptors or not, and ask if they can refer you to someone who can train you. Raptor handlers will be in contact with local conservation agencies and groups to provide educational programs about their birds, so these agencies and groups should have further information for you.
Choose your program and enter it. Choose one which will provide you with at least the basic care, feeding and handling instructions and teach you how to use the basic equipment involved, such as gloves and lures.