Go to a Local DMV office and get a CDL pamphlet and Study the Hazmat Portion Of it.

Go Here Pay the money and make a TSA interview appt.

https://tsaenrollmentbyidemia.tsa.dhs.gov/programs/hme

At the DMV tell a employee you want to add endorsements to your CDL. ( pro tip, get a tankers endorsement as well.. tankers endorsement is required by alot of hazmat companies in addition to double/triple endorsement)