@mdzh 

You should turn off WiFi in Archer C7 and only use WiFi from Deco.

Archer C7 router manages your home network (IP address allocations, etc., etc.) while Deco in AP mode covers your place with WiFi signal.

@Alexandre. If I turn off wifi on the archer how am I supposed to log into the management panel? Since the C7 holds my ISP settings, port forwardings and so on I might want to have access to those. How do I do that with wifi off? Only with ethernet?

@mdzh 

Before I answer that, please tell if you configured Deco WiFi with same SSID as Archer WiFi, or they have different SSID?

@mdzh 

If they have different SSIDs, the process is simple:

1. Connect wireless device you use to manage Archer (laptop, tablet, smartphone) to Deco SSID;

2. Access Archer management page from that device, you should be able to;

3. Turn off Archer WiFi through management page;

4. Your wireless device stays connected to Deco SSID and obviously you still have access to Archer management panel.

Done.

This is how my home network is set up: ISP router with its WiFi turned off, Deco running in AP mode, I have access to ISP router management pages on devices connected to Deco WiFi.

You can keep Archer router WiFi on, but you are going to have two strong WiFi signals, from Archer and from Deco, potentially interfering with each other. As long as you don't mind that, does not matter much.