From the Workout Builder you can click on the 3 dot stack to open the menu shown above to see the options for modifications. Broadly these break down into three different categories: Edit, Copy, and Delete.
Note: you may have to scroll up/down to see all of the options.
Edit: This opens the quick edit window which would be the same as a "Quick Add" where you can modify the Score Type, Title, and Workout Description.
Advanced Edit: This opens up the full detailed builder for the workout, the same as the "Detailed Add"
Copy Entire Day: Copy the entire day of workouts to another day.
Swap Days: You can take the current day and another day that you choose and swap them for each other.
Copy to Next Week: You can copy the workout you have selected to the same day next week. You can see a full tutorial of this here.
Copy to Date: Copy the workout you have selected to any date you choose.
Duplicate the Entire Week: You can copy this same week to another week that you choose.
For the copy options below you can choose which Workout Program to copy these workouts to as well as the day/date.
Delete: Delete the workout.
Delete Entire Day: This deletes the entire day of workouts.
Note: there is currently no undo option once workouts are deleted, copied, or modified.