Pushing off hard might work, but the official way is to use drill mode to log the laps
See this support page: Do the fenix 2/3, tactix Bravo, Forerunner 920XT, or Garmin Swim work for swimming drills?
For kick sets or swimming drills where arm motion is affected (e.g. kick sets, “catch-up” front call, one-arm swimming, sculling, etc.), these devices will not automatically count lengths and strokes accurately. When doing drills, it is recommended to use one of two methods.
The first method is to leave the watch paused when resting. This will prevent any erroneous data from being recorded.
The other method is using the drill feature to time the drill set and manually enter or confirm the distance. On some devices, it is necessary to enable the drill logging feature.
