I have changed my router/modem. How to integrate back my devices into the new router and network?

You can try one of the three following solutions:

1. Set the new router's SSID, password, and local router IP address to the same as your older one and the devices will reconnect automatically.

2. You can factory reset them and include them again in your new Wi-Fi network.

3. In the app, there is the "Wi-Fi batch change" function, but the devices must be connected to a Wi-Fi network for that, so you can try to temporarily create a Wi-Fi hotspot from your phone with the same SSID and password as your old router: