OpenWRT: Reconnect/Unbrick Archer A7 v5 (similar to C7)

I've configured the Archer A7 v5 to work with OpenWRT and it worked fine. I've used the TFTP method. Last week I tried to install a firewall on the run. After trying different methods. I found this guide copy-paste it -- see the print-screens below -- and since then the router is not accessible anymore. I mean: it starts, it shows that the wifi and the ethernet-cable are activated. However, it does not attribute any IP address regardless if you connect by ethernet or wifi. I know, I should not carelessly copy-paste if I do not understand exactly what I'm doing. However, I relied on being able to reset and restart everything. What I've tried After failing to connect by ssh or web-gui I've tried to reinstall the firmware via FTP-method. It doesen't work. Since I've done the initial installation 6 months ago I'm not sure if I might missing some detail. Additionally I moved from Debian to Arch-Linux and maybe there are some differences inside the network settings of my PC. Also the OpenWRT DD-WRT pages are somewhat contradictoriy about the specific settings. Like the required IP-address: a , b . Do you have some idea/experience about how to resolve the problem?