My watch won’t show temperature

I assume you are referring to the outside temperature using the Weather app. First, make sure it hasn't been deleted and is installed on the iPhone.

Delete built-in Apple apps from the Home Screen on your iOS 14 or later or iPadOS device or Apple Watch - Apple Support

Then add it as a complication to you watch face. See step r5 in the ';How to customize the watch face on your Apple Watch' section of:

Change the watch face on your Apple Watch - Apple Support

If the weather app is installed on your iPhone and Apple Watch:

On your watch face long press, then edit, scroll along the top to complications then chose your position and weather complication.

Please tell me if this method does not work😀