Problem Connecting Steam Link to PC with 2 Routers: Archer D2 & C25 Configuration Issues

I have a huge problem. Well, I have a problem connecting Steam Link to my computer. I have 2 routers at home and please look at the picture attached by me which shows what my network looks like - I drew in paint, so please be understanding :)

This is the case. If I connect Steam Link directly to the Archer C25 router, the PC is detected and works perfectly. Worse when I move the device to the main Archer D2 router. Can't see my PC. He tries and tries different ways in the Archer C25 configuration. The only thing I managed to do was that it detected and connected but my other router did not activate the internet so the PC also did not have a connection to Netia .. I did everything on the other router - from disabling DHCP to even MAC cloning etc - even changed connections from WAN to LAN - NOTHING and NOTHING . I have no more strength. Could someone kindly look at the instructions on this C25 router and help me configure it? http://www.tp-link.com.pl/download/Archer-C25.html here is the instruction.

I have no more strength. And I really want it to work. In the attachment I am sending a diagram of my home network. Do I have to configure something on the main router? Rather not.

Please help.

Set C25 as APek, i.e.
in C25
- disable DHCP server
- change LAN IP to abc187 where abcx is IP D2
- cable from D2 to LAN C25 port (empty port)

May God in children reward you! Everything works thank you!