If you would like to change your workout plan completely, you can do so from the settings menu. Visit settings by tapping the 'gear' icon at the top right of the Beyond. app screen.
If you would just like to update your existing workout plan, visit the home tab (home icon on the bottom left of the app screen) and find the week and date you want to amend from the top of the screen. From there you can select 'add workout' to add another workout session to your day.