Hallo and welcome to the site

It is great to hear that you want to make something of the next chapter of your life, but my personal opinion would be that without a much bigger investment of time and effort than you can probably begin to imagine, then this is not the right move.

Opinion is divided; there are those that believe that you can mug up on the subject and then go out and teach (rather like the old saying that there are those that do and those that teach). However, the overwhelming opinion seems to be that to teach the job well, you must first have experience, and that does mean real and ongoing experience. If you read some of the threads on here you will find that those that show the greatest insight into training have some professional background or long-term voluntary service experience, and in many cases are still working in an operational role of some sort.

There is no law stopping anyone from teaching first aid, even without any knowledge themselves. Listening to some experiences from people on some courses I have run, there are people out there who seem to do just that. If you want to train in the area where you can (try to) earn, you will need to be trained yourself first before you can do so under current regulations. There are companies out there who will take your money and give you a first aid certificate folllowed by a Trainer cert, but it won't necessarily make you a good trainer, and it certainly won't give you the real underlying experience. Good trainers also need to do lots of CPD and background reading, keeping up to date with developments not just in the UK but abroad, so it is not a static thing - I've learned the book so I'm set up for years now; that's not how it works even though it can be people's perception. Even with your certificate, you would be joining an overcrowded market, because first aid training is seen as a cheap and easy market to enter. If you are doing it for an income, you will be competing against the hobbyists and people doing it as a second job who have a main income somewhere else and will undercut you.

If you are still keen to proceed, I suggest join a voluntary service, get a couple of years decent and varied experience, get a few qualifications behind you, find a reputable Train the Trainer course and do that. But as you see, it won't be the quick and easy entry that many people assume it is.

Maybe not the answer you were hoping for, but it is an honest answer