Are you using the Firmware Restoration tool?
If not go to the
Asus Website and download it under Utilities. On the same page is the latest firmware you should download as well.
The rescue mode can be tricky to activate. I had to do it with my RT-AC87U, with the help from
this FAQ
Basically, do this:
- Press the Power button at the back to turn the router off
- Press and KEEP holding the Reset button for about 5 seconds
- KEEP holding the Reset button and press the Power butten to turn the router on
- KEEP holding the Reset button until the power LED flashes slow
- Release the reset button and connect your PC with a LAN cable to the router
- Set your PC's IP address to 192.168.1.10, Subnet mask to 255.255.255.0
- Start the Firmware restoration tool and restore to the latest Asus firmware you downloaded earlier
- Then upgrade to the desired Asuswrt-Merlin version for your router
Good luck!