Graded return to activity is your friend here.
About when to start: Today. But you may need to adjust your perception of training. If you’ve been bed bound for a week then today might just be walking about the house. Tomorrow might be a walk to the shops and back. The day after that may be walking to the shops and also a walk around the park, and so on. The best person to judge how much you do is you, the idea being that you do more each day without knackering yourself out so much that end up doing less the next day, that is just goung backwards.
So: judge each day’s level of activity with what you did the day before, not with when you were at peak fitness (obvious I know, but everyone does it!! 🙂 )
Enjoy! 🙂