@terziyski 

I tried several ways of connecting it but in the end I could only get it working by doing like this:

1. I reset the extender
2. Connect to it
3. Set device password
4. Select the 2.4 and 5 GHZ networks that I want to extend
5. "Applying your settings"
6. "Confirm Location" and Next
7. "Connect to your Wi-Fi" and "I´m connected"
8. Logging into RE305
9. More -> Operation Mode -> Access Point -> Save
10. RE305 rebooting
11. "Pull down to refresh or add a new device" 
12. No device found
13. Connected it directly to router via cable and tried again
14. Connection established
15. Turned off DHCP
16. Changed the 2.4GHz network name to the same as router Wi-Fi -> Reboot
17. Changed the 5GHZ network name to the same as router Wi-Fi -> Reboot
18 "Connect to your Wi-Fi" and I press "I´m connected"
19: Add password to 2.4 Wi-Fi -> Reboot

20. "Connect to your Wi-Fi" and I press "I´m connected"
21. Add password to 5 Wi-Fi -> Reboot

20. "Connect to your Wi-Fi" and I press "I´m connected"
21. Extender signals "Working Well"
22. Unplug it from the router and connect it to the switch -> after reboot signals "Working well"