I recently bought a TP-Link AC1200 Wifi Extender 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.

Same issue as someone else on the chats - I don't understand what any of the responses mean. Could someone explain in extremely basic steps what to do? I've tried restarting and unplugging so not that 

Thanks!