I've tried to read documentation and watch youtube videos about the Asus routers - the AC68U and RT-N12+ in this case, and try to understand the "Repeater mode" which they both seem to support (but the docs for the 68U doesn't include anything about it - seems to be supported only in the latest firmware). Here is a screenshot of what it claims to offer:

Feb 07, 2020 Extend Wi-Fi Network Using Old Router as Repeater Getting the Wi-Fi Details from the Main Router: The very first thing you need to do is … How to Extend Your Wifi Network With an Old Router Option 2: Use your router’s wireless repeater mode Look through your router’s settings (or manual) to determine if it has some kind of “wireless repeater,” “extender,” or “ bridge ” mode—yes, it’s Repeater mode – Keenetic

AP Mode(for hotel Internet extension) AP mode is more used to transfer wired connection into …

How to Turn Your Old Router into a Repeater - Make Tech Easier 2. Connect your router to a computer not connected to the network. 3. Go through step 1 again with the old router until you get to the configuration page. Copy the Settings from the Primary Router. Now you need to enter the information you copied from your primary router’s settings to the one you will now use as a repeater… How to configure Repeater mode of the Wireless N Access

Bridge Mode and Repeater Mode | Wilders Security Forums

Position a Second Router. When you set up a new router, place it near a Windows PC or another … Step by step guide to use a dd-wrt router as a repeater Take note of your the security settings of your primary network. For this, you will … Amazon®.com: WiFi Range Extender, 1200Mbps WiFi Repeater 1, The wifi extender mode of this device can be set up by wireless device such as smart phone or laptop. 2, Setup Repeater mode successfully beside router, and then move repeater to another place, thus lessening issues. 【Package Included】 1 x Wireless WIFI Range Extender Repeater 1 x RJ-45 Ethernet Cable 1 x User Manual Micro Center - How to configure an ASUS RT-AC68U Wireless