You can only change the pool size before you start your swim, in the goggles.

If this is your first swim, your pool size will be defaulted to 25m. If you have swum before, the pool size will be set to the last size you selected.

Select Pool Swim in the goggles using the front button. Then navigate using the rear button to select your pool swim mode (Up Next, another workout or free swim). You will then see the screen displaying the current pool size. You can press the front button to accept and continue, or the rear button to navigate to Edit. 

If you select to edit, you will then see the default pool size options which you can navigate through using the rear button. To select one, press the front button. 

The options you see will be: 25m, 25y, 50m, Set Custom.

After your swim, the swim's pool size will be offered by default on your next pool swim.

Custom Pool Sizes

• If you need a custom pool size, select “Set Custom” using the front button, then select meters or yards using the front button. 
• Select the first digit by pressing the front button, then use the rear button to select the number. 
• Press the front button to confirm, then the rear button again to navigate to the next digit. Repeat the steps as needed. 
• When done, press the rear button until you see “Confirm” in the display and press the front button.