How do I add a lap button to my workouts?

Hello,

Mark segments in your workout

If you want to mark a segment in your workout, double-tap the screen, then wait for the segment summary to appear on the screen. For example, in an Outdoor Run workout on a track, you could mark each lap or distance. In a 30-minute Indoor Cycle workout, you could split the session into three 10-minute segments.

To see all your segments after a workout:

1. Open the Activity app on your iPhone.
2. Tap the Workouts tab.
3. Tap the workout, then scroll down.

Because your screen locks during swimming workouts, you can't mark segments.

From:

Work out with your Apple Watch - Apple Support

If it's for running, the closest solution I have found is to use the Nike+ app on the watch, select speed workout and press the crown and side button at the same time for each interval. The only thing missing is average pace as it will show current pace. If you want to do active recovery, press the side and crown twice for each interval.

This method works far better if you change the watch orientation so that your thumb on your opposite hand can press both buttons at the same time e.g. I have the watch on my left wrist with the digital crown on the left side and press both buttons with my right thumb. This setup has the advantage of working in pouring rain rather than trying to use the touch screen.