How do I reconnect my robot vacuum after changing the Wi-Fi router?

Reset the vacuum’s Wi-Fi, not the router. Put the vacuum in pairing mode (usually holding the power or home button for 3-5 seconds until the Wi-Fi light blinks), then remove the old device in the app and add it fresh. Most cheap robot vacuums only work on 2.4GHz Wi-Fi, so temporarily disable the 5GHz band or create a 2.4GHz-only guest network. If it still won’t connect, reboot the vacuum and your phone, then try again — 9 times out of 10, forcing a re-pair fixes it.