@Lyner 

Hello, is the recommended network your host 2.4G WiFi network? if not, please select your host WiFi network and enter correct password.

If it stil stucks on the same step, please refer to the following steps:

1. Click “Exit Setup” to exit setup, go to the Devices page on the Kasa app to see whether you can control the bulb, if yes, go to the Device Settings page to change the device name and icon. If you can’t control the bulb, confirm whether the router has enabled "AP Isolation/Client Isolation" function or not.

2. Make certain the router’s Wi-Fi signal strength is strong, and the phone is connected to the same home Wi-Fi network as the smart bulb.

3. Make certain the Wi-Fi password of the router is correct. Password length cannot exceed 64 characters and does not contain characters such as single and double quotes.

4. Try other phones if you have.

5. If possible, try to change wireless channel (fix channel to channel 1, 6 or 11) of the router and start over again

In addition, what is the WiFi LED status on the plug after the setup? 

Hope it helps! Have a nice day!