You can make customizations like altering the colors or decide which statistics the clock face should display (depending on the installed clock face) in the clock faces settings in the Fitbit app. To get there follow these steps:

- Step 1: Open Fitbit app on your phone.
- Step 2: Tap the profile icon in top left corner.
- Step 3: Click on "Sync Now" to make sure that a valid connection between phone and watch is triggered.
- Step 4: Tap clock faces.
- Step 5: Tap on the clock face in which you want to change something.
- Step 6: Choose "Settings" and make the customizations.

Every successful change will be confirmed by the watch with a short vibration. If no vibration happens, try to choose your customization again or repeat the sync between watch and phone.

Normally the weather updates every hour automatically based on your location. If there is no or a stuck connection between phone and watch, the weather data cannot be transmitted to watch and temperature will not change or be displayed. In that case the watch will retry every 10 minutes to get a connection to phone and send the weather data again.

Sometimes a stuck connection can be resolved by a manual weather update, which you can trigger by following these steps:

- Step 1: Open Fitbit app on your phone.
- Step 2: Tap the profile icon in top left corner.
- Step 3: Click on "Sync Now" to make sure that a valid connection between phone and watch is triggered.
- Step 4: Tap clock faces.
- Step 5: Tap on the clock face in which you want the weather to update.
- Step 6: Choose "Settings" to open the clock face settings.
- Step 7: Tap on the red text "Refresh weather manually" in corresponding settings section (section where you can choose the temperature unit).  

Important for continues weather updates is that you have permitted the Fitbit app to use "always" your current location data and not only when the Fitbit app is running in the foreground. So make sure that you have this setting in your Android or IPhone set accordingly.

Moreover the weather is sent to your watch through the Fitbit app on your phone, so please keep it running in the background and do not manually quit the app.

If you are an IPhone user make sure that in the Fitbit app settings the following is set:
- Location: Always
- Background App Refresh: On
- Mobile Data: On

If none of the above resolves the issue, restart phone and watch and try the above steps again.  

If there is no or a stuck connection between phone and watch, the customizations cannot be transmitted to watch and nothing will change on the watch.

As a first step to resolve this issue try to synchronize you watch to phone in the Fitbit app again. If that does not resolve the issue, try to reboot your phone and watch and try customizing again.

You can change the time mode in your profile settings online at: https://www.fitbit.com/user/profile/edit
The Fitbit app does not have this setting. After you made the change, sync the watch with your phone in the Fitbit app and the clock face will consider the above settings.

Here a step by step manual:
- Step 1: Log into your "fitbit.com" dashboard and click the gear icon.
- Step 2. Choose "Settings" and afterwards "Personal Info".
- Step 3. Under Advanced Settings, find Clock Display Time and select the time format.  
- Step 4. Click Submit and sync your device.

Reasons for that problem are mostly:
- an out dated Fitbit app.
- a corrupted installation of the clock face or app
- a stuck internet connection of the app

To resolve the issue please make sure that you updated the Fitbit app to the most recent version from your app store (no updates for Fitbit app in Google Play Store or Apple Store available).

If you did and there is no update, try to restart the watch and phone. This step should resolve problems with the internet or Bluetooth connect between phone and watch.

Should the issue still be present, please try to reinstall the clock face by installing another random clock face and my clock face back again.

Check out this thread on Fitbit community forum to resolve issues with not completing installations: Clockface Installation Problem - Fitbit Community