TrainAsONE does not currently have any features to manipulate activity file recordings, and so there are two approaches to this issue. (3 if you include ‘doing nothing’.)
1. Override the duration and distance of the run. You do this on the Edit Activity page. This disadvantage of this method is that TrainAsONE can resort only to cursory activity analysis, and detailed information cannot be calculated. Consequently, if the run is an assessment, this will almost definitely prompt TrainAsONE to reschedule the workout.
2. The preferred approach is to use an external tool to crop the activity file and then upload this modified file into TrainAsONE.
For instructions on uploading your newly modified file, please see our How do I upload an activity file (recording)? FAQ.