There are three ways that I know of.
1 - The obvious one is go to college. In the UK, Newark, London, Leeds, Manchester, Glasgow all have college courses. The downside is that they can only teach within the experience of the teachers, and at the end of the course you will be 50% trained, 10% experienced but 100% unemployed.
Generally, these courses should be regarded as a starter pack for self employment, or perhaps as a repairer attached to a guitar shop. There are very few opportunities for employment as a guitar maker, and most established makers prefer to train their own staff.
2 - Don’t go to college, but find a job with an existing maker or repairer. With the right grovelling attitude and something special or unusual to offer, it can happen. Having accommodation, personal issues, and finances sorted out before hand helps a lot. Don’t expect to be taught everything about how to make a guitar - mostly, you will acquire just some of the skills, and gain some others by observation and listening.
3 - Teach yourself. There are lots of books and videos, and lots of old guitars to practice on. This approach is very slow and inefficient, but it works at your own pace and is a lovely hobby. As with college training, it might not help you obtain employment.
At the moment I have three staff plus myself, and I have no plans to take on extra help, but people do move on, and I like to be aware of potential employees for the future. From my point of view, previous experience or college training is a significant disadvantage, as it takes longer to un-train someone than to start from scratch. Woodwork skills can be very useful, but the most important ones by far are personality and attitude. Read all the comments in the previous section.