Hold MENU, and select Sensors & Accessories > Altimeter.

Barometer

Allows you to set the barometric pressure manually, or select a value from the nearest METAR station through the Garmin Connect™ app. Setting the current barometric pressure manually can help to improve the accuracy of the pressure altitude reading.

Altitude Alert

Sets an alarm to vibrate when you reach a specified altitude. The altitude alert is not available in watch mode.

Sync to Elevation

Allows you to synchronize the watch to your current elevation manually.

Set Standard Baro

Allows you to set the standard barometric pressure.