There is no way to manually turn off your Wyze Band. Instead, you can let the battery drain until it shuts off, or reset the band.
To factory reset and turn off your Wyze Band:
Tap on the Wyze Band screen, and scroll and tap the Setting screen. Scroll and tap Reset. When the 4-digit code to pair the device is shown, long press the Home button to display the Setting screen. Tap Power Off.
Related article: How do I factory reset my Wyze Band?