In general terms, presenting does not have a single definitive route into it. Ways in can vary from working in the industry in another role, as actors or models, some are experts in another field, others are journalists.
While there are presenter courses available, there is no guarantee of a job at the end of it. A good idea is to create a showreel to highlight presenting skills and then approach production companies for work. Showreels do not have to be produced professionally, many are self-shot and uploaded to social media sites. A number of agents specifically represent presenters - a quick search online will show you who they are https://www.spotlight.com/contacts. You could try them when you have a showreel.
Ultimately, presenting is a very competitive area so you should be prepared to be persistent.