There are two ways to approach this.
First, head into the individual milestone that is incorrect. There you’ll see three dots on the right hand side of the milestone you want to edit. Tap on those three dots and then edit the value. Remember, you’re only cheating yourself if you bump it up.
Second, reset your session by going into the session itself and tapping on reset session. Then you can adjust the ride file itself, with FitFileTools and then re-upload the workout.
All your progress data relates to your current plan. Once you’ve completed your plan, your progress data will be stored within the goal report.