There's this book and others, and you can take in person classes. If you can get in with a stagehand or rigging company that will let you work as a downriggers assistant, you can learn a lot on the job as well.
Entertainment Rigging for the 21st Century: Compilation of Work on Rigging Practices, Safety, and Related Topics https://www.amazon.com/dp/0415702747/ref=cm_sw_r_apan_i_1GQXNZ2SDZYFJ6XGTG60
Im not sure how good this book is but I have it in my wish list on Amazon