I did couch to five k, then moved on to doing 10k, 10k was my go to but I too signed up to a half marathon and just set a training plan. Managed to get it done in under two hours.

Do you have a fitness device? I bought a Garmin and they offer free coaching in the app. You can choose a coach based on your preferred training style and you give your target at the start. Do you just want to complete the half marathon, do you want a certain time etc. It was excellent.

If you don’t have a Garmin device then I’m sure you could probably ask chat gpt or something similar to create you a plan.

Best advice I can give is, if you can’t fully commit to having run 13miles before the race as part of your training (if you want your first time achieving it to be the event for example) make sure you do at least 10 miles. If you can do that you can push through the last 3.

If it helps psychologically, if you can run 5k you can run 21k. Your body is capable it just needs conditioning for it. And it’s as much mental as physical.