Answer by
LeheckaG (1826)
You can ask to apprentice/study under an existing-technician
(like at a dealer/repair-shop);
Find a trade-school offering appropriate-classes;
Enlist in the military;
or Read books, order supplies, experiment/practice, meet with experts (like at trade shows),
get a Federal (ATF.Gov) dealer or manufacturer license, start your-own-business,
and become self-taught.