This can (currently) only be done on your computer.
Open Training Plans and find the training plan you want to edit/change.
1 Click the menu icon on the right side of the training plan.
2 Select "Edit"
A: Click Add Practice. You will then get up choices for how exercise you want to add.
B: Click Create Own Exercise
Fill in and click Save. You have now created your own exercise. You will also find this under the Library tab (marked with your club's initials and a grey triangle in the top corner).