You can change a custom routine you created at any time. The way you open it for editing differs a little by device.
On Android
Open your custom routine, tap the menu icon in the top right corner, then tap Edit Routine.
On iPhone
There are two ways. Swipe left on your custom routine and tap the edit (pencil) icon, or press and hold the routine and tap Edit Routine.
What you can change
Editing opens the same builder you used to create the routine, so you can add or remove exercises, adjust each exercise's length, reorder them, rename the routine, and update the cover.
You can only edit custom routines you created, not Bend's built-in routines.