Hello Stinyo789,
Welcome to Apple Support Communities. To get started, let's try to reset your Apple Watch and paired iPhone:
Restart your iPhone - Apple Support
Restart your Apple Watch – Apple Support (AU)
If the issue persists, unpair, and re-pair your Apple Watch would be the next step. However, before you do, we recommend ensuring your Apple Watch is backed up as shown here: Back up your Apple Watch - Apple Support
Once you have a backup, check out our page for unpairing here: Unpair and erase your Apple Watch - Apple Support
When you re-pair your device, test dictation as you normally would. Let us know if the behavior changes.
Also check this out:
Run with your Apple Watch - Apple Support
We hope this information is useful. Kind regards.