After update my Apple Watch to 3.0, my workout app doesn't work. What can I do...?

Hi

What happens when you try to use it?

What steps have you tried to resolve the issue?

The following steps may help:

Restart both your iPhone and your watch, turning both off together, then restarting your iPhone first:

• Restart your iPhone, iPad, or iPod touch - Apple Support
• Restart your Apple Watch - Apple Support

Unpair and re-pair your watch:

• The Watch app on your iPhone takes a backup of your watch automatically when unpairing via the app. Choose to Restore from Backup during set up. Most data and settings will be restored, with some exceptions (eg Apple Pay cards, passcode).
• Unpair your Apple Watch and iPhone - Apple Support
• Set up your Apple Watch - Apple Support