Ensure that the sign has power first and foremost.
Ensure you are connected to the AP hotspot of the sign, or on the same WiFi network that the sign is connected to.
Next try power cycling the sign. Whether that is from the breaker or physically at the sign itself.
If the sign does not come back online after a few minutes, you can send an email to support@edgexled.com, and we will contact you to help!