Deleting liked workouts
Just click the heart like you did when you liked it.
From what i remember, to delete many things in skimble, i had to go online via browser on phone or on pc and go to my account on skimble dot com.
Otherwise, you can try unliking via the app, then clearing the cache, and if that doesn't work, deleting app data and logging back in fresh might work. App data is usually downloaded and saved and the removal function prob doesn't update the same as when you add a like.