You can use VoiceOver gestures to trim Camera videos and Voice Memo recordings.
Trim a video. While viewing a video in Photos, double-tap the screen to display the video controls, then select the beginning or end of the trim tool. Then swipe up to drag to the right, or swipe down to drag to the left. VoiceOver announces the amount of time the current position will trim from the recording. To complete the trim, select Trim and double-tap.
Trim a voice memo. Select the memo in Voice Memos, tap Edit, then tap Start Trimming. Select the beginning or end of the selection, double-tap and hold, then drag to adjust. VoiceOver announces the amount of time the current position will trim from the recording. Tap Play to preview the trimmed recording. When you’ve got it the way you want it, tap Trim.