Hello Alaniz,
Thank you for taking the time to let us know about your inquiry. I'm happy to shed some light on the situation here.
Changing a Wi-Fi network would leave your Nest Thermostat offline in the app unless it had been reconnected to it. To sort this out, you might need to reset its network by going to Reset > Network. This will disconnect your thermostat from the old connection, so you will have the option to reconnect it.
After it is refreshed, go to the Network settings and connect it to your new Wi-Fi network. Remove the thermostat from the app before attempting to add it. Please check out this article on how to change the Nest Thermostat Wi-Fi network and how to set up your Nest Thermostat.
Let me know if you need more help.
Regards,
Mark
