Thermometer icon shown while charging my watch

That seems to be normal behavior. When your Apple Watch gets too hot, it’ll stop some functions. Follow the steps in this article to make sure your Watch is being charged correctly.https://support.apple.com/en-us/HT204508

If you are following the steps and the problem persists, I’d recommend contacting Apple Support to look into repair and/or replacement options. Hope that helps you!

See this to help

https://support.apple.com/en-gb/HT204640

This might help you.............https://www.iphonetricks.org/apple-watch-temperature-warning-screen/