How can I add weather to my modular face watch?

Hello Sharart,

Welcome to Apple Support Communities!

We want to help you get the most from your Apple Watch.

We see you viewed the Apple Support page for Change the watch face on your Apple Watch - Apple Support

That link has the proper steps to add the Weather app complication to your watch face. See here:

"How to customize the watch face on your Apple Watch

1. Press the Digital Crown to go to the watch face.
2. Touch and hold the display.
3. Swipe left or right to choose a watch face, then tap Edit. 
4. Swipe left or right to select a feature, then turn the Digital Crown to change it. For example, you might change the color of the second hand or the markings on the watch face. 
5. Swipe all the way to the left to edit complications, which you can use to check things like the weather, your activity, or information from other apps that you installed. Tap a complication to select it, then turn the Digital Crown to review available complication options. Tap the desired complication to select it.
6. When you’re finished, press the Digital Crown to save your changes. 
7. Tap the watch face to set it as your current face."

We hope this helps to add the complication like you want to your Apple Watch.

Please let us know if you have further questions.

Cheers!