Hi
It is not possible to edit the results for a saved workout.
If you would like to submit a feature request to Apple, then you can do so here:
Feedback - Apple Watch - Apple
Note that Apple Watch can pair and sync with compatible gym equipment by following the instructions here:
Use gym equipment with Apple Watch
When recording treadmill-based runs, Apple Watch otherwise relies on data from the built-in accelerometer when estimating results including distance and pace.
When recording specific fitness activities, be sure to use the Workout app (or a third-party app that shares data to Health) and to choose the activity type that most closely matches your workout, including choosing Indoor Run for treadmill-based running workouts. This enables your watch to use the most appropriate sensors and data sources when tracking results:
For the most accurate results for treadmill-based runs, be sure to allow the arm on which you are wearing your Apple Watch to swing naturally as you are running.
It may also help to calibrate your Apple Watch, including resetting any existing calibration data.
Calibration teaches your Apple Watch how your arm movements relate to your stride lengths at different speeds when you are walking and/or running. It does this, during outdoor walk and/or outdoor run workouts that are recorded via the Workout app, by comparing data from the accelerometer with GPS (Location Services) data.
To calibrate your Apple Watch - and to reset existing calibration data - follow the instructions here:
Calibrating your Apple Watch for improved Workout and Activity accuracy - Apple Support
Resetting your calibration data and calibrating afresh can be equally as helpful for Series 3 models and will not erase your Activity history.