Buy, read and UNDERSTAND
"Regulator Savvy" ( www.scubatools.com ) and "Maintainance and Repair of Scuba Regulators" ( www.airspeedpress.com ) plus every regulator service manual you can find. Then buy several different types of regulators and service them. It's best if you start with those that you can get parts for, the Scubapro MK-2 and 5 and Sherwood Brute and Magnum are excellent piston regs, USD/AL Conshelfs are perfect diaphragm choices and if you can add a HOG, Zeagle or Apeks you have see almost all the different basic designs used for the last 40+ years. Not only will you have seen most all the current designs but you will also have several excellent regulators to dive. And finally, ask questions in the DIY section of SB, there are a lot of very good techs here.
None of the so called technician classes will make you "authorized" to service any particular brand. The manuf require you to take their own course and most of them you can not take unless you are working for a shop so to be an authorized tech you will still need to work for a shop. My experience with these classes is not good. At least the ones I have attended as quick overviews with little hands on and almost no theory so unless you are already a good tech, taking them is a waste of time....or worse yet you come out thinking you actually know how to work on regs.