Fix Ubiquity / Unifi Network set up (WiFi Access Points and Switch)

I have a Unifi Network already set up in an office. It has two access points (AP), one switch and one Wifi Extender. One AP works but the other does not appear to be working. When I try to adopt the devices in the Unifi Network Application, it says they are controlled by another controller or turned off. I need someone who knows about Unifi and how their Network Application works so that I can get these 4 devices back on the controller. Once that is done, I need you to make sure both APs are working correctly along with the Wifi Extender.