Hello SueD25,
Thanks for using Apple Support Communities. It sounds like you’re having trouble with the Nike Run Club app on your Apple Watch. We are happy to help.
To start, while the title of the article below may not seem to pertain to your issue, we suggest trying these steps:
If an app unexpectedly quits, stops responding, or won’t open - Apple Support
If that doesn’t help, try unpairing your Apple Watch and setting it up again. When you unpair your Apple Watch, it automatically creates a backup as long as you’re signed into iCloud on your paired iPhone.
Unpair and erase your Apple Watch - Apple Support
Set up your Apple Watch - Apple Support
Take care.