I recently bought a TP-Link AC1200 Wifi Extender (RE305) for my home. I got it connected to the router and have all the blue lights across the top. However, on my phone I keep getting an alert on my wifi that there is no internet connection. I have no idea how to fix this, so if anyone could give me step-by-step instructions (because so much of this stuff I just don't understand), I would really appreciate it.

Thanks so much in advance!