Go to training, because you can solve the problem in time with a professional teacher to explain it to you, so you can learn faster. The effect of self-study for several years is probably not as good as that of training for two or three months.
PLC is an engineering subject, and it needs a lot of practical operation to really understand this subject. If you teach yourself, the equipment is definitely not as perfect as the training institution.
Moreover, self-study is not suitable for everyone, because self-study requires strong self-control, is not affected by the environment, and is also very conscious, that is, the kind that can be learned as soon as possible. Even if you can't, you can study with the help of professionals. The key is that you are self-taught, where to find professional people to help you solve the problem.
Finally, learning any subject requires a systematic study of this knowledge. The knowledge learned by self-study is scattered, and it is difficult for ordinary people to learn without detailed plans.