Hey there CTC295,
If you tried changing the brightness from your Apple Watch, use the Watch app on your iPhone instead and try changing the settings there next:
You can also make these adjustments on your iPhone. Open the Apple Watch app on your iPhone, tap My Watch, tap Display & Brightness, then adjust brightness and text.
Adjust brightness, text size, sounds, and haptics on Apple Watch - Apple Support
Should the issue persist, check for updates on your Apple Watch and iPhone, install any that are available, then restart and test to see if the issue remains.
To update:
1. Make sure that your iPhone is updated to the latest version of iOS.
2. Make sure that your Apple Watch is at least 50 percent charged.
3. Make sure that your iPhone is connected to Wi-Fi.
Update your Apple Watch - Apple Support
If you need additional help, reach out to Apple Support directly: Get Support
Take care!