How to calibrate altitude on Apple Watch

The first (and simplest) thing to try if something isn’t working right is to restart your Apple Watch and its paired iPhone. If necessary (device not responding), try a forced restart. Both methods can be found here:

How to restart your Apple Watch - Apple Support

Restart your iPhone - Apple Support

If that doesn't help, the next steps would be to unpair and pair your watch again and restore from the backup just created. This should result in no loss of data. It deletes all temp and corrupted files and re-indexes the file system.

Unpair and erase your Apple Watch - Apple Support

Set up your Apple Watch - Apple Support

If the watch face has the problem, you should do a factory reset.

Unpair and erase your Apple Watch - Apple Support

You might want to delete and reinstall the app. Some metal in Apple Watch bands may mess with the altitude sensor.

So sorry that none of this worked. This may be a severe hardware problem. You may need to contact apple support to help you get it fixed.

Try this article:

https://wccftech.com/your-apple-watch-might-show-incorrect-altitude-readings-in-unusual-weather/