Step 1: Open the Session details
Step 2: Convert the Session
On bottom right of the Session details screen, there is a (+) button that will reveal additional options when pressed.
From that menu, find and tap the button marked “Convert to Workout”.
This will open a window, where you can give your Workout a name. Once you’re happy with your new Workout’s name – which can always be changed later – tap the Create button.
This will convert your Session into a Custom Workout, and it should appear at the top of your My Workouts on the Workouts tab.