Sorry to hear about your injury. Congratulations on your great progress in fitness. The good news is that your fitness will come back to its previous level a lot faster that it took to gain it in the first place. While there is no rule of thumb as where to start when you are able to train again. It is going to depend on who long you took off and your fitness. The most important thing is to start back conservatively, probably at a lower volume that you might want to. It’s way better to, at the end of the first 1-2 weeks training, to say: “I feel great and I think I can do more” Than it is to feel wrecked and need to take time off or get re-injured. Try starting at 50% for week 1 and seeing how you feel. Then adjust up to 60% if that felt easy and so on. Allow about as much time to regain your previous volume as you took off with the injury.