After 7 years, there have been so many changes to the site along with issues reported and resolved. It would be difficult to say whether or not the issue you're having today is the same.
Are you trying to edit the name, change the activity type, something else?
working with a Garmin Edge 1140 plus Forgot to turn it off till the next day 20 hours later Did 4hours 10 mins ride but time is 20 plus hours do data averages meaningless Just want to cut out the extra 16 hours Followed the instructions in Garmin Connect only to find that the Edit button does not allow Editing either on the application in Iphone or on Apple Mac IMac OSX
Just as described 7 tears ago
want to cut out the extra 16 hours
Use Garmin Connect Web and the "Trim Activity" feature: https://connect.garmin.com/modern
You'll be able to trim the activity based on time or distance.
Trim Activity - If you started an activity on your Garmin device too early or ended it too late, don't worry. Trimming your activity lets you remove unwanted portions for a more accurate view of your overall performance.
What is the Trim Activity Feature in Garmin Connect? | Garmin Support