How can I resend a push notification I previously sent using the web UI?

Currently, there isn't a direct "resend" button for push notifications that have already been sent.

To send the same message again, you have two options:

Recreate the message: Manually create a new push notification with the same content and targeting settings as the original message.
Use Presets: If you anticipate needing to send the same message multiple times, you can save its content and settings as a Preset before sending it initially. You can then easily select this Preset to send the message again in the future.