On an iPhone you should be able to merge workouts by turning the phone sideways in the calendar view and dragging and dropping the two workouts together. I used to be able to login to the mobile app and accomplish this but it seems you now have blocked website login from a mobile device. It’s impossible to login to the mobile website from a phone.

Had to dig but with a direct link you can still get there, although your cancel button should NOT redirect you to the app download. I am coming to the login page to access the website!!

https://app.trainingpeaks.com/