If you want a qualification, then it’ll be the first part i guess, but if it’s to learn the basics, as others say, spend 300 quid on tools and watch youtube, if you struggle then join a local club/group/etc, get out and about and ask for help in learning, always a few folk who know bikes well that are happy to help out, share tools, etc.
I tend to do everything, bar full suspension services myself, that’s down to cost though, tools are pretty expensive things if you want the whole lot, but you can get some decent starter kits for 100 quid and then build on that, again for 300 quid you can get a good amount of bike specific tools to do the jobs.