Hello 🙂 The main thing for me is to listen to your horse, don't go too quick and be progressive in your work.
You can start by adding one session in your week, two "normal" trainings and one lighter. You can add lunge and go outside with your horse, the best thing to do is to diversify your work so that your horse won't get bored.
When you add one training in your week, make sure you reduce the time your work, if you were used to ride 2x times a week, 1 hour, then if you ride 5 times a week you can ride 30min for example 🙂
Hope it helps x