It is currently not possible to crop your run data in PowerCenter. You can use the sliders in the graphs to highlight the part of the run you are most interested in, but not permanently modify it.
However, you can use an external editor to manipulate your run data and cut the part you want to remove or split your run into multiple sections. The recommended free tool is https://www.fitfiletools.com. Note that you can also combine files and other manipulations with FIT files (not all possibilities are covered here, contact support for assistance if needed).
- Export your FIT file in PowerCenter to your hard disk.
- If step one was successful, delete the activity from PowerCenter. Note that if the run you delete was factored into your CP in the past, the associated point in your CP history graph will disappear and will not re-appear after the edited upload.
- Open a tab in your browser, and open https://www.fitfiletools.com
- Follow the instructions on the web page (use the section remover tool). Save the file from fitfiletools to your hard disk. If you want to split your run data, just repeat this step so that you end up with two separate files.
- In PowerCenter, go to the Calendar Tab and press the top right corner to upload a run. Upload the files saved in step 4. Your modified run data will now appear in PowerCenter.